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Home My WebLink About09-15-16, Dickinson, City Growth, Public Comment ME= Leave no city behind lose to 4 billion people live in cities.As the driver how this broader global urban agenda unfolds. of environmental challenges,accounting for near- Many organizations are already assessing sustain- 1 ly 70% of the world's carbon emissions, and as able urban development: multilateral bodies (e.g., UN- j sites of critical social disparities,with 863 million Habitat and the World Bank),city networks(e.g.,United dwellers now living in slums,urban settlements Cities and Local Governments and C40 Cities Climate are at the heart of global change.This momen- Leadership Group), academia (through the Interna- tum is unlikely to disappear,as approximately 70 tional Council for Science), think tanks (e.g., Adelphi), million more people will move to cities by the end of this and foundations(e.g.,the Prince's Trust).Indeed,there is Michele Acuto year alone. The good news is that recent multilateral no shortage of urban expertise,but there is little clarityis director of the processes are now appreciating this key role of cities and about how concerned and knowledgeable parties might City Leadership are increasingly prioritizing engage.The NUA's zero draft Initiative and urban concerns in policy- points to evidence-based 3 making.Yet,how can we en- policy as critical to its suc senior lecturer R sure that these steps toward cess and proposes an Inter- at STEaPP, a global urban governance - national Multi-stakeholder University leave no city,town,or urban - Panel on Sustainable Ur- College London. dweller behind? banization, led by UN-Hab- Email:m.acuto@ > The third United Nations Q itat. Some experts suggest ucl.ac.uk;Twitter: (UN) Conference on Hous- creating an even broader @Pacioz ing and Sustainable Urban g' monitoring body, akin to an Development (Habitat 111) � "IPCC for cities."Others urge will set out a "new urban caution and raise concerns agenda'(NUA)this October about scientific input. The tx in Quito, Ecuador. Twenty SDGs, Paris agreement, and �'� ,ry years after Habitat II, the Sendai Blamework all call NUA aims to inspire nations, for data that are increasingly wcities, and towns to pursue spatial (e.g., geographic in- sustainable urban develop- formation system-based) Susan Parnell is ment. Habitat III's focus rather than statistical (e.g., z on cities reinforces recent demographic)to achieve the a professor in the wider multilateral attention `;..urban settlements are at the granularity that is necessary Department of to cities through the Sendai �� to understand cities. Environmental w PY•amework for Disaster Risk heart Of global change. Data-gathering capacity and Geographical Reduction,the 2030 Agenda is underdeveloped,weak, or Sciences and the of the UN Sustainable Development Goals (SDGs), the dysfunctional in many parts of the world.Building credi- African Centre Z Addis Ababa Action Agenda on financing sustainable ble local data systems requires strong governmental data for Cities at the P development, and the COP21 Paris climate agreement institutions and university-city collaborations that,with University of [including a call for a city emphasis by the Intergovern- the increasing influence of large private-sector interest Cape Town,South mental Panel on Climate Change(IPCC)], and capacity,are rarely in place.Africa,Asia, and Latin Africa.Email: w Despite these good efforts,and the potential for Habi- America are especially data(infrastructure)poor.There susan.parnell@ tat III and the NUA to coalesce action,the road ahead is no consensus on who should set metrics,who might uct.ac.za is complex. Consensus that cities are critical pathways generate and monitor data, or what the architecture of of change does not indicate agreement on what the pri- the science-policy interface underpinning global urban orities should be,how they are assessed,and how policy governance should be.Implementing a global monitoring and implementation might be refined. The envisioned mechanism for cities acknowledges that there are trans- assimilation of city,national,and international indicators national drivers of urban change and embraces the idea o to track progress across sectors and scales is far ahead of that the way all cities are run will determine our com- the science-policy capability on the ground.Until recently, mon future. If the Post-2030 Agenda logic of"leave no there was limited discussion of any practical approach to one behind"is to incorporate the logic of "leave no city achieving and assessing the transformations required.Yet behind;'then fundamental attention to fair, accessible, the metrics selected to track progress,and the credibility and effective monitoring and mechanisms is imperative. N of the organizations that implement them,will determine -Michele Acuto and Susan Parnell z 0 10.1126/science.aagl385 0 x SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 873 ii This is purely a thought experiment. It may not be as big news as it sounds.99 Harvard University biologist George Church to STAT,on criticism that a 10 May meeting he co-organized on synthesizing a human genome was not open to public scrutiny. AROUND THE WORLD Microbiome initiative launched WASHINGTON, D.C. I President Barack ObaAtmospheric C0 reaches a milestone out.a new plan cross-disciplinary weekdroller 2 out.a new plan to fund cross-disciplinary u projects that would study microbes in all Earth's environments,including the human body.The National Microbiome Initiative would commit$121 million—from fund- ing already appropriated and included in the president's 2017 budget request—to microbiome-focused grants at NASA, the Department of Energy,the National Science Foundation,the National Institutes of Health,and the U.S.Department of Agriculture.Private foundations,com- panies,and academic institutions have pledged another$400 million in research funding.The initiative aims to unite scien- tists from diverse fields to develop tools for understanding the function of individual microbes and mapping how they interact in communities.http://scim.ag/M icrobel nit Everest experiment cut short MOUNT EVEREST, IN NEPAL I UK.moun- taineer Richard Parks has prematurely Earth has passed an unfortunate milestone. Last week, carbon dioxide ended his team's expedition to the summit (CO )levels at Cape Grim,an observatory on Tasmania in Australia,rose of Mount Everest,where he planned to above 400 parts per million(ppm),according to scientists with the court- take the highest ever blood sample and try's Commonwealth Scientific and Industrial Research Organisation. muscle biopsy(Science,I April,p.14).Parks and his team had first climbed smaller Cape Grim is one of three baseline observatories in the Global peaks to acclimatize to high altitude,but Atmosphere Watch program of the World Meteorological Organization, a blood test taken last week at the moun- W along with stations in Mauna Loa, Hawaii, and Point Barrow, Alaska. tain's Base Camp(5380 meters)showed a The measurement was expected: CO2 measurements at Mauna Loa that the acclimation was too much of a first surpassed 400 ppm in May 2013 and have topped that number good thing.Parks's body was producing U every year since.But Northern Hemisphere observatories are subject to large seasonal cycles (see inset graph) 410— because of the push-pull between ' CO2 emissions from burning fossil fuels 390 . 400.2 and the uptake by plants in spring and ~ry 385.0 summer. In contrast, Cape Grim has a r very small seasonal cycle—so if it's 400 370— _cape Grim Day at Cape Grim,it's 400 Day world- ' Mauna Loa wide. Scientists estimate that 20C of 350— global warming will occur at 450 ppm. 0 2010 2015 http://scim.ag/Grim400 F s MEN Richard Parks being monitored in April. 874 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE INSIGHTS PHYSICS The Big Picture On the Origins of Life, Phil osOphy for pi�ysicistts Meaning Universse Iand the tself,Itself ' Sean Carroll A cosmologist explores the philosophical implications of the Dutt n,2016.480 pp. foundational laws of nature it By Barry Loewer "consistent,"but I think he means something fill in the details in The Big Picture make for stronger, along the lines of"their claims are a lively research project in physics and phi- he 20th-century philosopher Wilfrid entailed by fundamental physical laws and losophy(2). Sellars characterized the aim of phi- facts:'Thus,although generalizations in eco- Another challenge is understanding how losophy as"to understand how things nomics may be the best way of talking about thought, consciousness, and free will fit into in the broadest possible sense of the changes in the money supply,true economic physical theory. Thoughts are"about"things term hang together in the broadest generalizations about the money supply must outside themselves,consciousness possesses a u possible sense of the term."This is also be defined by the laws of physics that describe "what it is like"feel,and free choice seems to physicist Sean Carroll's aim in his new book, the motions of elementary particles and the involve decisions that originate in an agent.It The BigPicture.He sets out to show how var- fields that constitute the distribution of mon- is difficult to see how these are entailed by the ious phenomena,including thought, choice, ey and the rest of the economy. motions of fields and particles.Carroll discuss- consciousness,and value,hang together with Carroll observes that the laws of physics es a number of well-known arguments that at- the scientific account of reality that has been are complete within the domain of physics, tempt to show that such phenomena are in- developed in physics in the past consistent with a purely physical 100 ears. He attempts to do fundamental ontology and right- all this without relying on spe- ly concludes that these are not cialized jargon from philoso- persuasive. But poetic natural- phy and physics and succeeds ism should not be satisfied until spectacularly in achieving both it can include an account of how aims. these elements emerge from fun- Carroll calls his view"poetic damental physics or, if such an naturalism,"the latter of which account is not forthcoming,why consists of two parts. First, he they do not involve nonphysical argues that observation and the fundamental ontology. scientific method are the only re- A related challenge has to do liable ways of learning about the w. with understanding the place of world. The second component value in the big picture. Carroll is that the systematic applica v follows Hume and noncognitiv- tion of the scientific method has ists in ethics,arguing that value taught us that there is one natu claims are not descriptions of ral world that,at a fundamental objective aspects of reality but level,consists of quantum fields "What is the fundamental nature of reality?"asks Sean Carroll in The Big Picture. rather that value is invented by distributed in space-time, the human beings.But it is not clear distribution of which is subject to physical meaning that any change in the configura- that this view does justice to the way we think laws.Currently,these laws are those of quan- tions of fields and their particles can be ac- about ethics and value. tum field theory and general relativity. Any counted for in terms of earlier configurations A last challenge that poetic naturalism 1 future physical theory is expected to subsume and fundamental laws. He argues that it should seek to address is why the universe these two tenets as correct in their respective follows from the structure of quantum field has the laws and parameter values it does domains. theory and the results of particle experiments and exactly how one is to understand what it The"poetic"part of Carroll's view refers to that all the fields and forces that are respon- is to be a law. Carroll does not answer these the idea that there are many true descriptions sible for the behavior of macroscopic objects questions,but he does argue that theological of the world,including those contained in the are known.Because any process must be im- explanations and metaphors are of no help. special sciences,the languages of psychology, plemented according to fundamental physi- Recently, a number of prominent physi- economics, ethics, poetry, and so on. In any cal laws, it follows that this is sufficient to cists (Feynman, Weinberg, Hawking, and particular context, our purposes determine exclude certain kinds of putative phenomena Krauss)have dissed philosophy, claiming ei- the best way of talking. (e.g.,astrological and paranormal influences) ther that it is of no use to physicists or that o For Carroll,attempts to describe the natu- from reality.Carroll does not mean that these the problems it addresses have been solved ral world are legitimate as long as they serve are a priori impossible but rather that they already by physics. The Big Picture shows the intended purpose and the claims made in are inconsistent with established physics and why these claims are misguided. Fthem are consistent with the established theo- so are ruled out by poetic naturalism. REFERENCES ries of physics and with each other. He says There are challenges to poetic naturalism 1. S.Carroll,From Eternity to Here:The Quest for the Ultimate N that need more discussion than Carroll gives Theory of Time(Dutton,London,2010). them.One is the origin of"times arrows,' es- 2. See,for example,D.Albert,TimeandChance(Harvard Univ. a The reviewerisatthe Rutgers Center for Philosophy and the Press,Boston,2000). PP Sciences,Rutgers University,New Brunswick,NJ 08901,USA. pecially causation.Carroll first addressed this a Email:toewer@rci.rutgers.edu issue in a previous book(1),and his efforts to 10.1126/science.aaf6858 SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 903 i s 3 1' MEW s 904 20 NlAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE u By Nicholas S.W.- g ton,Julia Fahrenkamp-Uppenbrink, ' *a4 w bl+ ,and David Malakoff NEWS Rise of the cityp.906 arth has becoe an urban planet.—M©" ,, ,than half of the world's Roots of the urban mina p.sos m p now live in,cities and the ro ortion is growing. And A plague of ratsp,s�2 people g g' China rethinks cities p.916 urban areas are sprawling even faster;than'they are adding Vancouver's green dream p.sre people,swallowing up both farmland and wildlands •.•....• ••• .. .•1.•... The implications are sobering.The land area neededto provide REVIEWS city residents with food, energy, and materials is expanding; City-integrated renewable energy for urban sustainabilityp922 this ecological footprint is often 200 times greater than the area Emerging solutions to the water of a city itself. The resulting carbon emissions, added to those challenges of an urbanizing world from cities themselves,mean that urbanization is now the main p 92s driver of climate change. ' PERSPECTIVES The rise of cities is not, however, all doom and`gloom. By some Transport solutions for cleaner metrics, consolidating human populations helps shrink our individual airp,934 The ecological future of cities p.936 environmental footprints, and cities are serving as laboratories for Living in cities,naturally p.938 further improvements. Researchers are exploring creative approaches Meta-principles for developing to harvesting urban waste streams, integrating renewable sources of smart,'sustainable,and healthy energy,and improving transit. cities p.940 Hidden linkages between This collection of Reviews, Perspectives, and News features, as Well urbanization and food systemsp.943 as interactives you;can find at http://scim.ag/lTbOWdZ, delves deeper Building functional cities p.946 into how we came to live in cities and what urbanization means for the "........................... """". .. ." future of our planet and ourselves. One message is clear: The urban RELATED ITEMS! ►EDITORIALP.873 planet is here to stay, and the decisions we make today about how we .LETTERS P.886 build and live in cities will affect generations to come, ►PODCAST ►VIDEO httpJ/Scim.ag/lTbOWdZ ail m> d b ,P E 10 v° 1990 r' q 100 ; yo§ t o 2014 50 10 a._ 800 ` a p 2050 �t, France so �' 1990 t I: 40 _ r 1' 20 100 2014 Percent population 50 " in cities 40,000,000 _ a µ 10,000,000 0 2056 * w �r:;2 100,000 United States 41 city population 1990 100 ek 2014 , 50RISE OF \ ........... THE CITY 0 2050 Paraguay .". In 2014,54%of the world's population,or 1990 3.9 billion people,lived in urban areas.That's up 100 from one-third in 1950,and forecasters say the pro- 2014 portion will rise to 66%by 2050.More than half of \ w urbanites live in cities of fewer than 1 million people, 50 _� z but there are 28 megacities of more than 10 million. y As they sprawl,cities displace species,alter water and geochem 0 2050ical cycles,and reshape landscapes. `"�= Namibia Z 0 U a Where the wild things were People like to live in many of the same places favored by wild plants and animals,such as rich coastal plains and river valleys.Asa result,cities of more than z 200,000 people(blue)are expanding in many of the world's richest biodiversity hot spots(orange).And as many cities sprawl across the landscape faster than their populations grow,learning to manage this competition for prime real estate will be key to protecting many species;including our own. w Oz a_ 00 1950 Africa had a relatively 2025(projected) small urban population in Cities will encroach Z the mid-20th century. on many of Asia's Q • wild areas.'' 0 t. ...•�. d 'ate. •.. • & 'e"°� � � z L a•- �o c� One of Africa's Central most biodiverse °• America's key regions will host migration y some of the corridor was world's fastest ® o Z largely rural, growing cities. 906 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE tA URBAN PLANETSECTION Urbanization's hard truth Cities alter the environment in many ways,from creating air pollution and unusually warm"heat islands"to producing noise and artificial light.One of the most dramatic ecological changes is caused by the spread of impervious surfaces, such as paved roads and roofs.The hardening prevents � water from soaking into the soil,promoting flash floods and w, polluted runoff that damage aquatic ecosystems. f , A study of nine U.S. 50 cities found a close link w between urbanization ® ® i and hardening... v, 40 c E ffi s 1990 100 � � 30 Q 2014 +, .. 50 10 r r., 0 2050 China 0 XV 0 20 40 60 80 100 1990 Percent urban development 100 2014 - ��- 25 d ® ...and that even low levels 50 N of hardening can do damage 20 to populations of aquatic z organisms,such as insects. 0 0 2050 E India 15 Li v I 1990 l' 100 c 10 2014 g 50 5 0 0 2050 Q 0 z Australia 0 20 40 60 80 100 0 z Percent urban development Q The changing geography of urbanites In 1950,most of the world's city dwellers were in Europe and the Americas.But Asia and Africa now host the world's largest and fastest growing cities. w Cities in just three nations—China,India,and Nigeria—are expected to add nearly 1 billion residents in coming decades,with most of the growth occurring w in cities of fewer than 1 million.By 2050,nearly 75%of urbanites will be in Asia and Africa. 0 0 G 0 •OCEANIA NORTH AMERICA LATINAMERICA EUROPE ASIA AFRICA 100..._,.1.1u/o.. 0.7% 143% 6.2% 80 60 (J 0 c o a' Q U r_ 40 L U d a Z0 ..,. Q 2M E .. 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 907 SPECIAL SECTION URBAN PLANET r r ROOTS OFTHE r f v" The stress of living with strangers may have spawned cherished aspects of city life By Greg Miller tuff a Stone Age human into a time everybody else, which made it possible to hamlets grew big enough to be called cit- machine and put him on the New keep track of who was most likely to help ies.In this view,aspects of city life like fash- York City subway at rush hour and you during a hunt—or kill you in your sleep. ion and public architecture developed long his mind would be blown,if not by Today more than half of us live in cities,sur- after agriculture, as a byproduct of life in the speeding train, bright lights, rounded by multitudes of people well never large groups. and strange smells, then by the meet.It's a radical change,and it happened But overcoming food constraints is only sheer concentration of people.One in an evolutionary eye blink. We navigate part of the story, according to evolutionary crowded subway car might contain our increasingly urban modern world with psychologist Robin Dunbar of the Univer- more human beings than he'd ever Paleolithic brains. sity of Oxford in the United Kingdom,who come to know in a lifetime spent hunting In the traditional view, agriculture was has synthesized his own and others' work and gathering on the grasslands of Africa. the innovation that paved the way for cit- into a novel hypothesis about the origins w For the vast majority of our history as ies.About 12,000 years ago in the Neolithic of urban life. He argues that in addition to a species, humans lived in small, mobile period, early farmers figured out how to getting enough to eat,the first villagers had communities of dozens to perhaps a cou- grow enough food to feed many people in to leap another equally significant hurdle: o ple hundred individuals. Everybody knew one place, and eventually some of these the cognitive demands and social stresses 908 20 MAY 2016•VOL 352 ISSUE 6288 Sciencemag.Org SCIENCE a, r m 3 i i �r 0 K= f 5� Most people who meet in the Xingu people's village square in Brazil already know each other.But in a large city,people must share space with millions of strangers. a created by living in the midst of strangers. DUNBAR Is BEST KNOWN for the number mans solved this problem by living in fission- "The stress of living in large communities that bears his name. "Dunbar's number"is fusion societies that break up when they get is very, very intense," Dunbar says. "It's a the number of significant social relation- too big, much as modern hunter-gatherer major problem all primates face.You need ships that one individual can maintain.He groups do today. But something changed in mechanisms that will defuse the situation argues that it's determined by the brain's the Neolithic,allowing humans to begin liv- and allow you to stay together." capacity to store information about indi- ing in much bigger communities. Dunbar,who is best known for provoca- viduals and relationships. In primates, the Dunbar began thinking seriously about tive research on social networks, thinks number correlates with the relative size of this question a few years ago, after partici- Neolithic people invented,or at least stum- the neocortex,the folded sheet of tissue on pating in a multidisciplinary project funded bled on,just such mechanisms.For example, the surface of the brain (Science, 5 October by the British Academy in London called architecture that designates certain spaces 2012,p.33).For chimps,it averages about 45, Lucy to Language. He and archaeologists for certain types of social interactions helps according to Dunbar's analysis of published Clive Gamble of the University of South- people know what to expect when entering field studies. ampton and John Gowlett of the University a new building.Material trappings like jew- For humans it's something like 150.That's of Liverpool, both in the United Kingdom, elry and pottery signal the social group and probably not everyone you know, but it's led a team that examined the published status of strangers.And religion and elabo- the friends you'd most likely invite to your archaeological record for clues to the evolu- rate group cultural rituals, like singing or wedding. Dunbar says the number emerges tion of human social life.If psychological ad- dancing together, act as social glue among again and again in a handful of direct tests justments were crucial to the dawn of bigger people in large groups,he says. and in data from sources as varied as the settlements,they would have preceded or ac- "It's a brilliant synthesis,"says anthropo- number of recipients on Britons'Christmas companied them,rather than appearing only logist Richard Sosis of the University of card lists, the size of Roman infantry divi- later in well-established communities.In re- Connecticut (UConn), Storrs, of Dunbar's sions,and the number of Facebook"friends" ports on Near East Neolithic settlements,the idea. "Like any good theory it unites dis- with whom people actually interact. researchers began to see hints that mecha- parate observable facts and enables you to In a small group,it's possible to remember nisms for relieving the social stress of living ask new questions." each individual and their reputation and con- in larger communities emerged early. Yet Dunbar's ideas have gotten a cool nections to the rest of the group. In groups One set of strategies utilizes physical reception from other anthropologists and larger than Dunbar's number,it's impossible objects to make social interactions with archaeologists, many of whom wouldn't to keep track, and that's incredibly stressful strangers more predictable and less scary. even comment for this story. They don't for all social primates,Dunbar says.He cites Imagine walking into a coffee shop in a see the need to bring in psychology,saying several lines of evidence,including findings strange city.The space is filled with Strang- that there's plenty of evidence that agri- that crowding reduces fertility in captive and ers, but the layout is familiar. There's a culture drove larger, more permanent hu- wild primates,and work suggesting(though counter and behind it a guy in an apron. man settlements.Inferring the mental states perhaps not conclusively)that violent crime He's the barista, obviously, and you know of prehistoric humans is tricky business, and mental illness are more prevalent in big how to interact with him even though you and Dunbar's account will be difficult— cities(see paper in this special issue,p.938). don't know him.You place your order,hand but perhaps not impossible—to test. For most of our history as a species, hu- over money,and step aside so someone else SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 909 # wggr �* j � ti `j 1 a v VL IWAII kr X I l SY/ t � t Xt 7h t{ s " E � � $ � � B r can do the same. Everyone knows their number of social categories. As Gamble, and interactions. For example, at Beidha, role. The thousands of such interactions who was Coward's postdoctoral adviser, an early Neolithic site in Jordan,Byrd and that happen in a day mostly go smoothly, puts it, "Material culture had to become colleagues have found what appear to be because they're so predictable. more complex if we were going to expand dwellings for individual families, often ar- That's how material culture, including without losing our sanity." ranged around a central public space.Indi- uniforms,helps make life among strangers Architecture may also have served as a vidual dwellings often had areas for storing more manageable today,says archaeologist social aid, Dunbar and Coward argue in a grain or other resources—among the first Fiona Coward of Bournemouth University, chapter in a 2014 book called Lucy to Lan- signs of private property—but food prepa- Talbot, in the United Kingdom, who also guage: The Benchmark Papers. The ways ration and other cooperative activities were worked on the Lucy project. Its roots go Neolithic people arranged their spaces sug- done in public.Dividing the space like this back to when people first started living in gest the development of new forms of social would have helped limit and formalize so- large groups,she says."What we see in the life, Dunbar and Coward argue, drawing cial interactions,Byrd says."Dunbar's ideas Near East as people start to settle down is support from the work of others,including on psychosocial stresses dovetail nicely an elaboration of material environments." anthropologist Brian Byrd,who has studied with my perspective.' Coward has spent several years combing the transition to more permanent settle- The same forces may have been at papers to compile a database that includes ments in the Near East and U.S.West. work at Qatalhbyiik, the largest and best- roughly 30,000 humanmade objects dis- Most of our clues about our hunting preserved Neolithic settlement, in mod- covered at nearly 600 Neolithic sites in the and gathering ancestors come from people ern Turkey (Science, 20 November 1998, Near East.She's been tabulating objects and who live that lifestyle today,explains Byrd, p.1442).There,starting 9500 years ago,peo- their styles,from tools like awls to decora- a primary investigator at the Far Western ple built enclosed dwellings that sealed off tions like beads, to track the development Anthropological Research Group, a cul- life inside from outside eyes and let inhabit- and spread of material culture at these sites. tural resources consulting company, and ants control who came in."Qatalh6ydk is an The conventional thinking is that people a research associate at the University of extraordinary site because the houses are settled down first and then started accu- California, Davis. Visit the hunting and built close together like cardboard boxes, mulating more stuff, but Coward thinks it gathering Mung people of southern Africa, bang up against each other,"says archaeo- may have been the other way around. Her for example,and you'll likely find buildings logist Trevor Watkins of the University of preliminary analysis suggests that at many made from brush that offer little privacy. Edinburgh, who has worked at the site. (though not all)sites,rich material culture "In their huts, the doors are wide open, "You moved around on the flat roofs and preceded the growth of settlements. If so, they all face the center,and the hearths are from there you descended by ladder into material culture may have enabled larger out front,"Byrd says."Everybody's business the building,"he says."It's very deliberate— communities rather than merely being a is everybody's business." you couldn't just walk accidentally into byproduct of them. The growing diversity The lack of a distinction between public someone's doorway." of tools, jewelry, and figurines helped de- and private space may work for people in In a place like Qatalh6yiik, which was lineate social roles, Coward says. Instead small groups who know each other well, home to up to 10,000 people, there must of trying to keep track of hundreds or even But as people transitioned to larger, more have been conventions about whether you thousands of individuals, people could permanent settlements, they began treat- knocked on a door or asked to be let in,or o lump their neighbors into a much smaller ing distinctive spaces for different activities whether you approached a certain house at 910 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE URBAN PLANET SPECIAL SECTION People gathering to pray at a Jakarta mosque(left) may not know each other,but they are united by religion and dress. Similarly,ancient religion may i have eased social stress among hunter-gatherers who met at the ancient site of G6bekli Tepe in Turkey. "The idea that something like singing can bond larger groups makes a lot of sense,' says Sosis of UConn, who notes that this fits with his observations of Micronesian communities, where communal song and dance are reserved for festivals when people may, gather from other islands, NOT ALL THE PIECES of Dunbar's broader thesis fit together quite so neatly,however, and some researchers point to gaps in the -> evidence.Primatologist Joan Silk of Arizona State University, Tempe, for example, isn't convinced that social stress is such a big obstacle to living in large groups. Among chimpanzees,as groups get bigger individu- als do spend more time grooming to main- tain social ties,but they also have to range over greater distances and expend more energy to find food, Silk says. Thus their group size may be limited by food rather all given your social connection with the in- and dancing, practices that Dunbar has than psychology. "When groups split, it habitants,Watkins says.People would have argued strengthen social bonds. He thinks could be because the energetic costs of liv- needed new rules to navigate this emerg- these activities act much like social groom- ing in large groups becomes too high or ing social world, and Watkins thinks the ing in monkeys and apes,promoting bonds because the quality of social ties has been buildings themselves could have served as through the release of endorphins, the eroded," Silk says, "It's hard to say which a guide. "There are norms of behavior em- brain's natural version of opioid painkillers. plays a more important role from the avail- bodied in the architecture and the way the In a 2012 study published in the jour- able evidence." buildings are organized and the imagery nal Evolutionary Psychology, for example, The same question applies to Neolithic they contain." Dunbar and colleagues found that drum- humans. So far, only patchy evidence sug- ming, dancing, and singing in groups in- gests that mechanisms for overcoming so- OTHER INNOVATIONS helped people cope creased volunteers' endorphin levels, as cial stress emerged before humans massed with another potential contributor to so- measured by testing their pain thresholds together. That leaves plenty of room for cial strife: freeloaders. In groups smaller with an overinflated blood pressure cuff the traditional view that the richness of than Dunbar's number, everyone belongs or an ice pack. Active participation was objects, architecture, and culture arose to the same social network, and peer pres- crucial—pain tolerance did not rise when almost by accident after agriculture freed sure alone keeps people on their good be- people merely listened to music, people from spending all their time secur- havior,Dunbar says.In larger groups,more They also tested the next step—whether ing food. In this view, says Peter Turchin, formal rules and policing mechanisms music promotes social bonds—using a an evolutionary anthropologist at UConn, become necessary. London-based choir group. Members prac- "Agriculture happened and then social Other researchers have come to similar tice in groups of 20 to 80 and then come complexity just sort of bubbled up! But conclusions, and a growing number have together once a year to perform as a"mega- Turchin thinks Dunbar is right to chal- argued that religions with all-seeing, pun- choir"of more than 200.(Dunbar notes that lenge this chronology. "It's a bit contro- ishing gods arose to take over this policing these numbers approximate those of fission- versial,but I actually buy his idea:' role in bigger societies (Science, 28 August fusion societies in which small bands of Many of the Neolithic innovations that w 2015, p. 918). Dunbar says his thesis fits hunter-gatherers periodically live together Dunbar credits with aiding the transition with their research."Hunter-gatherers don't for a time.)In both the small and large choir to larger communities are conspicuous in have moralizing gods,"he says. The timing groups, members had higher pain thresh- our cities today. In fact, they're some of works: Archaeological evidence suggests olds after singing, and they reported more the things we most associate with urban Q that the Ilse of organized religion coincided positive emotions and stronger feelings of life, from elaborate architecture and cul- with or even preceded the emergence of inclusion and connectivity.The before-and- tural institutions to a dazzling selection of larger,permanent communities. For exam- after difference in social closeness was more material goods. If Dunbar is right, it's not ple, at Gobeldi Tepe, an early Neolithic site pronounced in the megachoir,the research- so much that we need cities to produce all z in modern Turkey, archaeologists suspect ers reported last year in the journal Evolu- these things.It's that we couldn't have cities z hunter-gatherers came together en masse tion and Human Behavior, suggesting that without them.: o for rituals before they lived together in vil- cultural phenomena like national anthems laces(Science,18 January 2008,p.278). and religious music promote social bonding Greg Miller is a science and technology Those rituals probably involved music in large groups of strangers,they said. journalist in Portland,Oregon. SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 911 SPECIALSECTION URBAN PLANET A PLAGUE OF RATS U �f �G Se. 2,1 y e r u„x- / 1 As more people crowd into urban slums,the risks posed by rodent-borne diseases are on the rise By Warren Cornwall, in Salvador,Brazil;Photography by Mauricio Susin ats haunt the slums of Pau da third largest. Many residents carry anti- Bautista. Six years ago, his 22-year-old wife Lima. Their paw prints sur- bodies for Leptospira,a bacterium found in died,unexpectedly,from lung damage caused round drain pipes. Burrows pock rat urine that can be deadly to humans. by leptospirosis. Soon after, Bautista sent dirt walls. Shriveled black feces "There's so many rats.You can't believe it. his son to live in the countryside with his speckle patio edges. The rodents Outside,inside; says Carlos Bautista as he grandparents. "It's better to have him alive even leave their mark in the sits on the step of his brick shack,looking there than to have him here"exposed to rats blood of the people living here in out over a pile of sodden trash and a make- and disease,he says in a voice barely above a crowded favela on the edge of shift chicken coop. a whisper. this sprawling coastal city,Brazil's The haunting is deeply personal for Rats have long been one of the world's 912 20 MAY 2016•VOL 362 ISSUE 6288 sciencemag.org SCIENCE d most ubiquitous—and infamous—forms spent much of a year tracking the outbreak, comfort.The uniforms serve as a white flag of urban wildlife, synonymous with pesti- The results,spelled out in a 1999 article in of neutrality to the drug-trafficking gangs lence and squalor. They've attracted only The Lancet, were among the first alerting that control these neighborhoods. Still,the sporadic attention from scientists,however, the world that this infection had moved to scientists are constantly on guard,watching Much about the secretive city rat—chiefly cities.Over 8 months,they found 326 severe for police entering the favela,often the pre- the Norway rat, Rattus norvegzcus— cases,with 50 people dead, and traced the lude to a gun battle. remains a mystery.But as the world's urban cause to a strain of Leptospira found pri- Ecologist Arsinoe Pertile, a graduate population surges and more people crowd marily in rats.They noticed that infections student at Salvador's Federal University of into rat-plagued neighborhoods like Pau da surged after intense rains,and that most of Bahia(UFBA)here,walks past shacks cling- Lima, the rodents are getting renewed at- the sick came from favelas on the city's out- ing to a hillside of red clay.Brassy rhythms tention from researchers and public health skirts, nearly half of which had open sew- pump from stereo speakers, melding with experts. Over the past decade,scientists in ers.One was Pau da Lima. the whine of saws and the bang of Kam- a number of cities have launched efforts to Beginning in 2001, that neighborhood mers,a testament to the constant construe- better understand rat behavior and evo- became the focus of an ambitious attempt tion of improvised dwellings in a place the lution, and the role they play in spreading disease. One of the most intensive and longest-running investigations into rat-human interactions is occur- 1� ring here in Pau da Lima, a chaotic °# { jumble of buildings astride a small, . hilly swathe of this city of 2.9 mil- : , lion people. For the last 2_decades, researchers have scrutinized the " bodies,homes, and habits of favela residents—rat and human alike— while dodging encounters with gun- toting gangs.The goal is to decipher the forces driving leptospirosis, which kills some 60,000 people an- nually worldwide,and find the best ways to curb a disease that experts �n 3 warn is an underappreciated threat in the burgeoning slums of a more urban world. "When we think about the slums ' in Jakarta or Manila or Cali,Colom- bia,what you see in Pau da Lima is i exactly what you see in those areas, if not worse,"says Albert Ko,a phy- Researcher Arsino6 Pertile performs a necropsy,collecting tissue samples that might reveal whether rats of a sician and infectious disease expert certain age or sex serve as particularly important disease carriers. at Yale University,and a founder of the Salvador research project. "We need to to merge infectious disease research,urban scientists have dubbed Valley 4. This and find out what solutions can be done imme- ecology,and community development.With several neighboring ravines are home to diately that are also generalizable to many backing from Brazilian and U.S. funding more than 3000 people squeezed into less of the urban slums." agencies, the scientists recruited local of- than a fifth of a square kilometer—a popu- ficials and favela residents to help under- lation density twice that of New York City. IKO'S INTEREST in Pau.da Lima's rats dates stand and counter the disease. Nearly 90% of the residents are squatters. back to 1996, when a surge of deathly ill The result has been pioneering work on The average person survives on the equiva- people, many with failing kidneys, started a disease so neglected that it doesn't even lent of$2.60 a day. appearing at the Salvador hospital where make some lists of neglected diseases, says At the valley floor, Pertile enters a he worked. At the time, leptospirosis was physician Joseph Vinetz of the University cramped,walled courtyard that serves as a considered a rural disease. The corkscrew- of California, San Diego, who studies lep- tiny open-air market,selling beer and other shaped spirochete that causes it dwells in tospirosis. `As far as I know, there are no drinks. There, a cage trap tucked between the kidneys and urinary tracts of rats and systematic urban studies like the one going a washing machine and a stack of empty farm animals, and it infects people when on in Salvador." bottles has captured a new addition to her their skin or mucus membranes come in research: a fist-sized ball of dull brown fur contact with water contaminated by the ON AN APRIL MORNING, a dozen re- with a pair of shining black eyes. animals'urine. Many people show no sign searchers wearing long white lab coats slip That afternoon, Pertile will kill and of infection, or just fever and aches. But a through gaps between buildings lining a dissect the rat, recording its size and sex small fraction develop severe kidney dam- traffic-clogged street, then descend steep and taking tissue samples. Among other age or massive bleeding in the lungs, al- paths into Pau da Lima for a day of data things, its urine will be checked for Lep- though researchers aren't sure why. gathering. The coats are sweltering-in the tospira. "Close to 80% (of the rats) had Alarmed, Ko and Brazilian colleagues damp, tropical heat. But security trumps Leptospira' during one recent research SCIENCE Sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 913 SECTIONSPECIAL URBAN PLANET sweep,she says, examining the caged ani- specifically untreated sewage and runoff.It her husband,who works as a garbage collec- mal as the shop owner calmly sweeps the connects everything in the favela—the rats, tor,always has a positive blood test. floor nearby.Researchers hope to help pin the bacteria,and the people. Given the abundance of rats and Lep- down the chief reservoirs of the bacteria Even in wealthy cities,rats can be rife with tospira in the slum, why doesn't everyone by correlating rats' age, sex, and capture Leptospira infections,but the number of hu- here get sick?Ko's team would like to know site with Leptospira levels in the urine. man cases is low. That's probably because Understanding why Nascimento and her Some rats may be more important carriers modern infrastructure steers most sewage kids dodged the bacteria, while her hus- than others. and rainwater—and Leptospira—into pipes band didn't,for example,could,offer clues The traps are part of a much broader ef- and away from people,says Federico Costa, to strategies for coping with the dangers. fort to construct a detailed picture of the an ecologist at UFBA who now directs the Overall,researchers have found that ap- faveWs rats.To identify hot spots of rat ac- Pau da Lima work.Not so in Valley 4.Open proximately 3.2% of the faveWs residents tivity,for instance,scientists have scattered sewers are the norm.The months-long rainy are infected every year. One in 30 of those throughout the valley hundreds of plastic season turns paths to muddy streams and infections leads to mild sickness, and one squares the size of dinner plates, coated floods homes in the valley bottom. in roughly 200 causes severe illness,based with a sticky film of soot mixed with methyl A few hundred yards downstream from on the number of cases admitted to the alcohol.They record a visual impression of the courtyard market, researchers crowd city's hospitals. every paw and tail that passes over them, into the small living room of one of those A string of studies published in the last On this day,Pertile and her research part- homes. Jamile da Cruz Nascimento, her 3 years lays out key risk factors. Houses ner, Luciano Lima, a rat exterminator for husband, and their three children live in with signs of rat infestation are nearly the city, are particularly interested in how the disease's bullseye—in a low spot, near twice as likely to have a Leptospira infec- quickly rats are repopulating Valley 4 after a the confluence of two sewage-filled streams. tion,for instance.Other factors are barom- recent extermination effort— eters of poverty. The danger and where they are coming increases the farther down- from. Genetic studies have hill someone lives, tracing found that rat populations in the slum's economic pecking each of the favela's valleys are order, which has pushed the relatively distinct,suggesting f poorest residents into the the rodents don't straytoo far. lowest, wettest areas. One Now, with traps at 60 spots study found the chance of in- in three valleys,they hope to 7 fection fell by half with every learn whether rat numbers additional dollar a day a per- are rebounding because the son earned. animals are moving in from neighboring slums,or simply THE LINK between infec- because Valley 4 survivors _ tion and water suggests that are reproducing.The answer { killing rats alone won't be could help shape future rat enough to protect Pau da control programs. Lima's residents. "People are The market is emblematic _ very close to the sewage and of how intimately people and For nearly 2 decades,the favela of Pau da Lima has a been a focus of urban rat research. very close to the rats," Costa rats coexist here. The build- says. "I think if it could be ing is perched at the edge of a stream of Flood waters can reach almost to her door- done,a system that collects most of the wa- gray,fetid water,fed by trickles from white step.Her sons often go barefoot or wear flip- ter...would avoid most of the infections." plastic pipes jutting from nearby build- flops rather than closed shoes;their skin is But in the favela,that's a big"if."In the ings. It's the valley's improvised sewer sys- constantly exposed to polluted water. early years of the project, scientists and tem. Empty plastic bottles and food bags Asked how serious she thinks leptospiro- community leaders successfully lobbied litter the streamside, tossed there rather sis is,Nascimento gives it a 10 out of 10.She the federal government for $36 million to than carried on the long hike to the top of pegs her risk of getting it as a five out of five. build a road and sewer lines through some the valley. A friend who lived nearby died from the dis- of the most flood-prone parts of Valley 4 Lima, a 7-year veteran of the rat wars, ease several years ago."We have many cases and a neighboring valley, as well as new points out the water,food,and thick vegeta- here,"she says."It's very serious." housing for 271 households,or about 7%of tion that make this a rat haven. He traces A small electric fan wags hypnotically the population.But today just a fraction of the route the rats can take from the stream- back and forth as a researcher slides a nee- the project is built.A tidy row of apartment bank,up through a drain pipe and into the dle into the arm of Eric,Nascimento's lanky, buildings sits empty along a freshly paved back of the bar. Within 4 months of the 12-year-old son. Dark blood courses into a street at the lowest end of Valley 4. But last extermination attempt,the valley"was vial, to be tested for signs of recent Lepto- sewage still flows down an open stream.In again full of rodents,"he says. spira infections.Another worker questions the adjoining valley,the only sign of work the boy:Has he had a fever or joint pain in is a dirt road running down a hillside. DECLARING WAR ON RATS might seem the last year?No.How often has he recently Delays ate into the funding,the research- the obvious way to address a rat-borne dis- walked in floodwater? Frequently. Did he ers say.And in 2015, gangs controlling the ease. But the Pau da Lima study has also wear rubber boots?Sometimes. other valley shut down the construction shown that killing rats isn't always the So far,Nascimento and her children have there,fearing it would give police easier ac- answer. That's because researchers have gotten good news: They've never shown cess. "That project should have been done realized another major culprit is water, signs of a Leptospira infection.But she says 10 years ago,"Ko laments. 914 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE �r ti �.r r: s r �r � y 5 i i I f t Researchers question Pau da Lima residents Jamile da Cruz Nascimento and her 12-year-old son Eric as part of their effort to understand disease risks. G GIVEN SUCH DIFFICULTIES, the scien- and the politically connected complained, Zoonoses:'They are responding to a report tists are looking for cheaper, quicker ways Ko says. Today, in contrast,the city focuses that a 12-year-old boy had come down with a y to make inroads against leptospirosis.They on 11 neighborhoods with the highest lepto- fever—perhaps leptospirosis. want to know how to fine-tune extermi- spirosis rates. In 2015, exterminators went The agents fan out into the valley to hunt nation campaigns, and whether things as house to house in five of the worst areas, for signs of rats and distribute poison. Last simple as fencing off certain areas,or giving leaving poison where they found signs of year,the cityhad five ofthese vans and a staff everyone rubber boots,could help. rats.When a case of leptospirosis is reported of 120 conducting extensive, neighborhood- The researchers hope to first test such anywhere in the city, a team applies the wide campaigns, says Maria Gorete interventions using a computer model that same treatment within 200 meters of the Magalhaes Rodrigues, who oversees the simulates how people, rats, and the bac- patient's home. city's rat program.But with the arrival of the teria commingle in the favela. Right now, Ko admits that they don't yet have data Zika virus, four vans and 80 workers were the model—being developed by Costa and confirming that such strategies reduce infec- reassigned to fight mosquitoes.Now,her rat scientists at Yale and the University of Liv- tions. But"my gut feeling,"he says, "is that team responds only to reports of infections. erpool in the United Kingdom—is relatively we have to figure out ways to reduce the "Leptospirosis is not taken as seriously as ' coarse; researchers can run scenarios only rat population." it should be,"she says through a translator. at the level of a whole valley. Eventually, Then she switches briefly to English: "But I they hope to be able to see patterns at a AMORNING spent with the city's rat patrol, fight for leptospirosis:' much finer scale,just tens of meters. however, offers a glimpse into the difficul- After less than 20 minutes of rat hunting, Still, insights from Pau da Lima are in- ties of brute-force extermination. An aging the agents in Valley 4 suddenly retreat up the fluencing city government practices.Fifteen Volkswagon van parks on a ridge above hill and back to the van.It turns out one had years ago, for instance, Salvador's rat con- Valley 4, and eight people spill out, wear- seen a policeman and feared bullets might trol efforts were haphazard,often centering ing white and blue polo shirts emblazoned start flying.Valley 4's rats,it seemed,would on affluent neighborhoods where residents with a logo reading"Centro de Controle de be safe for the moment. SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 915 I p . i w � a K` vrx. l h-. o S s M i r , a ,ee URBAN PLANET SPECIAL SECTION CHINA RETHINKS CITIES After decades of recIdess growth, the country revises its vision By Dennis Normile,in Guangzhou, China ust a few steps separate one of the to be evolution,not revolution;'predicts Yang and ring roads radiating ever farther fiom worst examples of China's recent Li,an urban planner at the Guangzhou office city centers. Zoning laws fragmented cities urbanization from one of the best. of the Institute for Ilansportation&Develop- into single-use residential or office districts. Tianhe Road,a main arteiy here in ment Policy(ITDP),which promotes sustain- Later,gated compounds with a few high-rise China's third-largest city, is eight able urban development.But over time,entire towers in huge,parklike settings leapfrogged lanes wide but snarled with cars. cities—not just isolated neighborhoods—may far beyond transit lines and other services. Pedestrians squi y between bland come to resemble Liuyun Xiaoqu. In a vicious circle, the spread of car- office towers and huge malls. Only dependent superblocks"quickly caused[traf- the brave ride bicycles. IN 2014, the World Bank described China's fic] congestion, so the government made Just a block away, pedestrians and cy- urbanization as "unprecedented in scale." more and wider streets," says Dongquan clists rule. Liuyun Xiaoqu is a verdant He, an environmental scientist at En- neighborhood about 5 kilometers from g ��- ergy Foundation China's Beijing office. the city core where small streets once _ Researchers estimate that superblock clogged by cars have given way to walk- __ residents use 65%to 80%more transit ways and planters.Boutiques,cafes,and energy than those living in mixed-use, groceries cluster at ground level in the walkable neighborhoods. midsize apartment buildings. Even on A perverse incentive exacerbated a drizzly day,the neighborhood is alive sprawl: Many governments depend with window-sho ers retirees and pp �-�-�=" `�� "� � on revenue gained by incorporating young couples. Residents can stroll to _ farmland and then selling the building stores, schools, and restaurants, and rights. "The revenue from these trans- many work nearby. It's a striking con- actions can amount to 40%or more of trast not just with the surrounding city, a city's budget,"Qian Zhang, a geogra- but with newer residential areas on the _— �' pher at the Chinese Academy of Sci fringes of town,where people live in gi- ! J 1 d a#j i ences's (CASs) Institute of Geographic gantic superblocks,isolated from work- Sciences and Natural Resources Re- } places and amenities,and rely on cars. search in Beijing,and colleagues wrote Guangzhou is not unique.China's ur- in 2014 in Land Use Poli l ban population doubled between 1978 I The result: Cities have sprawled and 2010 while the area covered by faster than populations have ._��, grown, g cities tripled.The sprawl has driven up so that "average population density ... car use and helped make China's cities a dropped by more than 25%;'the World major source of carbon emissions.Chok- — Bank estimates, while air pollution ing pollution and sedentary lifestyles increased. Shanghai's carbon dioxide are harming urban health. P (CO)emissions hit 13.1 tons per capita N Officials have concluded that the in 2011,higher than the 2013 CO emis- country's urbanization has gone awry ray sions of 5.7 tons per capita in London This past February, the State Coun- Guangzhou's bus rapid transit line(bottom)cut emissions,saved and the 8.3 tons per capita in Los Ange- Fcil and the Communist Party's Cen- travel time,reduced operating costs,and smoothed out the traffic les,California,according to a 2015 study z tral Committee—the nation's highest jams seen before the system was built(top). by the Lawrence Berkeley National z authorities—adopted new guidelines Laboratory in California."Reducing the Z that call for compacter cities with denser net- Less than 20%of China's population lived in urban carbon footprint is a key" to China 2 works of streets,more pedestrian and cycling cities in 1978; by 2014, more than half did. meeting its Paris Agreement pledge to reduce olanes, better public transport, mixed-use The bank and others noted that China's ur- greenhouse gas emissions,He says. zoning,and more green space."This is a sig- banization helped lift hundreds of millions Public health is also at stake.In big cities, 0 nificant turning point for Chinese cities,"says of people out of poverty. But they have also the incidence of chronic metabolic, circula- Yan Song,an urban planner at the University critiqued the new cities as unsustainable, tort', and respiratory diseases was roughly of North Carolina,Chapel Hill. Planners initially opted for Soviet-inspired double rural rates in 2008, according to a Experts warn that transformation will be wide streets,huge blocks,and massive build- study by Yong-Guan Zhu,a biogeochemist at difficult, and could take decades. "It's going ings, and then added U.S.-style highways CASs Institute of Urban Environment in Xia- SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 917 SECTIONSPECIAL URBAN PLANET men.Air pollution contributed to 1.2 million premature deaths in China in 2010, accord- ing to data extracted from the 2010 Global Burden of Disease Study. Reconfiguring China's cities along the lines of Liuyun Xiaoqu will be part of the so- lution.Built in the 1980s,the area began as a strictly residential,gated compound with about 6500 apartments.In 2000,residents gained ownership—and greater control—of e their apartments. Entrepreneurs opened e shops in first-floor units. The area is near a major stadium,so Guangzhou spruced it l up before the 2010 Asian Games with re- surfaced walkways,pocket parks,and play- s ' grounds. Gradually,Liuyun Xiaoqu opened its gates and restricted cars. Commercial and residential property values have risen more quickly than in surrounding areas,ac- cording to an ITDP study. "The beneficial policies were very simple, but they had a snowball effect,"says C.C.Huang,an urban policy analyst at Energy Innovation,a con '44- - sulting firm in San lZancisco,California. Guangzhou's bus rapid transit (BRT) - system offers another lesson. Gaining at- tention worldwide for their efficiency and — low cost, BRT systems have dedicated bus - lanes that are typically located in the center of a roadway to avoid curbside jams.Many BRTs have a single platform between two lanes,requiring special buses with driver's side doors.But GuangzhoVs has dual plat- forms, allowing the use of regular buses that operate beyond the BRT corridor. Opened in 2010,the BRT runs for 23 kilo- meters along a main east-west artery°Dur VANCOUVER'S - ing peak periods, 350 buses carry 26,900 passengers an hour, more than most of China's subway lines.The BRT will cut CO, emissions by 86,000 tons and particulate emissions by 4 tons annually during its first GREEN DREAM 10 years, ITDP estimates. Building a BRT costs about 10%of the price of a subway. The city wants to dramatically shrink its China is also looking to its past for a les- o son in sustainability. "China used to be the environmental footprint, but obstacles loom bicycle kingdom,' Song says.But in what she a calls one of the biggest mistakes of China's By Kenneth R.Weiss, in Vancouver, Canada urbanization, many cities removed once ubiquitous bike lanes.Now,they are restor- o ing them, Leading the way is Hangzhou, which operates the world's largest bike- ith apracticed eye,Innes Hood with Stantec Inc. LL sharing program,with 65,000 bikes. snaps a thermal image of a Hood's camera is taking aim at one of Remaking China's cities won't be easy. window-walled condomin- Vancouver's biggest challenges in its quest z Calls to open gated compounds, for in- ium tower dozens of floors to become the greenest city on the planet: o stance, have drawn fierce opposition from high. The glass glows white improving the energy efficiency of build- residents worried about traffic and privacy. hot, a signature of wasted ings.In part because of leaky windows and w People have grown attached to cars."It will heat radiating into this port poor insulation, buildings consume nearly be difficult to drive them back to public city's chilly air.Concrete and two-thirds of the energy used in the City of P transit,"Song predicts.Governments,mean- steel slabs also shimmer Glass—a nickname referring to Vancouver's while,will need to cooperate on transit and with the telltale rosy colors of waste. The landmark towers offering stunning ocean r other projects that are"complicated techni- slabs "are not insulated, so they act like and mountain views.Now,city leaders have tally," He warns. But he is optimistic that radiating fins," says Hood, a Vancouver, pledged to cut energy use and greenhouse o China is"moving in a good direction."n Canada-based sustainability consultant gas emissions from existing buildings by 918 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE r �.r x 22 r j s m Red reveals heat leaking frommaa tower in downtown Vancouver in this image,which combines a visual light photograph with a false color thermal scan.Energy-wasting buildings that radiate heat pose one of the biggest challenges to the city's effort to slash energy use and curb greenhouse gas emissions. 20%by 2020,and to require structures built Action Plan that has made it a prominent And an ample supply of hydropower from after 2030 to produce no net emissions.It's pioneer in urban greening, including ef- British Columbia's rivers has helped give part of a long-term goal of fashioning a city forts to transform raw sewage and food Vancouver the smallest carbon footprint of that operates entirely on renewable energy waste into energy, and to coax residents any major city in North America. and produces little waste. to use less water and leave their cars to Still, when Gregor Robertson ran for Vancouver isn't the only metropolis set- walk, bike, or ride public transport. De- mayor in 2008,he believed the city could do ting formidable targets.Around the world, spite some successes, however, research- even more.The provincial legislator and co- urban leaders are embarking on an array ers say Vancouver's experience illustrates founder of the Happy Planet organic juice of efforts to reduce the strain that cities the sobering limits that cities face in act- company pledged to make Vancouver "the place on the environment. Although cit- ing on their own to reduce environmental greenest city on Earth:' It was a winning ies are often seen as a source of environ- impacts,given the complexities of national message for voters. Once elected to office, mental problems, many analysts argue politics and a globalized economy. Robertson assembled a task force that la- they are also key to solving them; large bored for 2 years before issuing the 2011 ac- urban populations, for instance, can use BORDERED BY WATER on three sides, tion plan,which laid out a host of specific, far less energy per capita than rural or Vancouver squeezes more than 600,000 1 measurable targets. suburban residents—if the right policies residents into its city limits—and is the Much of the plan is far from sexy, deal- and infrastructure are in place. But time heart of a sprawling metropolis of 2.3 mil- ing with the nitty-gritty of quotidian city is short: Experts say that by 2050, about lion. Its downtown hosts the headquarters life,such as how to improve trash disposal, two-thirds of the world's population will of numerous timber and mining compa- transit operations,and building codes.Still, live in urban areas, and how cities handle nies, reflecting a region that has relied on the blueprint has helped catalyze real, al- rapid urbanization will be critical to pro- resource extraction for jobs and income. beit limited,progress. tecting biodiversity and human health, as Despite this economic history, a green well as combatting climate change. By one thread has long run through Vancouver's WALKING AHEAD of a rumbling garbage estimate, the world's urban areas could fabric.In 1971,the city gave birth to Green- truck in an alley in East Vancouver, Jez prevent the release of 45 gigatons of car- ! peace, the no-holds-barred environmental Figol peers inside a green city waste bin bon dioxide—more than eight times the group. In 1990, it became one of the first meant for food scraps and other organic annual emissions of the United States—if cities to officially recognize the threat of cli- waste. Discovering a misplaced milk car- the building boom over the next 15 ,years mate change. City Hall has long embraced ton, she pulls out a warning sticker and produces more efficient infrastructure, packing more people into the central city, slaps it on the bin. She adds the address Vancouver has taken the urgency to a strategy once termed "ecodensity," with to her clipboard of those violating Vancou- heart, In 2011, it adopted a Greenest City the aim of using fewer resources per capita. ver's tough trash-handling rules,which are SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 919 M.. _ � I t w , J r 1 L efl x s , wM . To cut methane emissions from its landfill,Vancouver strives to remove and compost all organic matter from its waste stream,producing a soil amendment. designed in part to reduce the amount of amendment for farmers and landscapers, by four companies. City officials estimate methane, a potent warming gas, burping Initially, compliance wasn't what city that each rent-a-ride removes as many as from the city's landfill. leaders hoped.Then they had a bright idea: 11 private vehicles from the road. Figol, a no-nonsense woman who used to switching trash schedules, and picking up Mostly, Donner bikes to work. He gets a investigate dog bites,is one of two inspectors the smelly, fruit fly-attracting green bins thrill when he passes a sign that displays who spend their days digging into garbage every week,instead of every 2 weeks."That the number of bikers that have pedaled by cans to crack down on careless residents did it,"says Albert Shamess,the city's direc- a bridge leading to downtown. "I'm a sci- who don't properly separate their waste.The for of waste management. "We saw a 40% entist so I love data,"he says. "I go out of city has expanded its recycling program for reduction in garbage and a 60% increase my way to trip the bike counter."Last year, paper, glass, and plastic to include other in composting." it recorded 1.37 million bike trips.Now,he items. It also requires wood removed from Still, Figol needs to remind some resi- wonders:"Will we beat that this year?" pre-1940 houses to be reused, recycled, or dents of the rules. In the alley, she finds a Survey data show the city has already burned as an alternative fuel. Vancouver's trash bag stuck in the wrong bin. She at- met the 2011 action plan's goals of cutting landfill, like many others, uses extraction taches a large red tag—so the drivers would kilometers driven per person by 20% and wells to capture the methane produced by leave it—and confronts a startled mother, coaxing residents to make half of their trips bacteria breaking down the trash. Most kids in tow,who emerges from the offend- in the city by foot,bicycle, or mass transit. of the collected gas is used to heat nearby ing address. "It's our job to do face-to-face But that success has brought strains: The greenhouses that grow tomatoes year- education," Figol says. And if that doesn't city's bus and subway systems now bulge round.The surplus is burned in a gas flare, work,next come fines. with commuters during the rush.Already- Despite these efforts, however, officials packed buses often speed past passengers figured that 40% of landfill methane was WITH THE WAVE OF A KEY FOB, Simon queued up in the rain. This being Canada, escaping into the atmosphere, where it is Donner unlocks a silver Fiat 500 parked in a the buses display signs that apologetically far more powerful at trapping heat than car-share spot below City Hall."I've always read:"Sorry,Bus Full." carbon dioxide. So they took another step, wanted to try one of these," says the geo- trying to remove all organics from the waste graphy professor at the University of British VANCOUVER is the first city in North stream. In 2013, volunteer "ambassadors" Columbia here. The city makes it easy for America to mine sewage for heat. Disking fanned out across the city, handing out him to not own a car, a bonus for this cli- up a sweet-smelling mist,a stream of waste- kitchen pails and instructions to toss plate mate scientist who likes to walls the talk.It water races under a catwalk in a concrete scrapings,uneaten meat,bones,soiled pizza has invested heavily in bike lanes and mass basement,and then through a giant strainer z boxes, and yard trimmings into the green transit, and claims to be the car-sharing removing big particles that might gum up bins. All this and more now goes to two capital of North America,thanks to a fast- the works."There's a lot of wasted heat go- composting facilities,which turn it into soil growing fleet of short-term rentals offered ing down the drain,"says Chris Barber. 920 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE URBAN PLANET i SPECIAL SECTION town buildings to invest $100 million to goals. Officials in Nanjing, China, won an switch from natural gas fuel to"clean wood award for electrifying the city's buses. But ° tA "0 .. waste" leftovers from the timber and con- the switch won't do much to reduce overall struction industries. greenhouse gas emissions,because 70% of China's electricity comes from coal, notes NEW POWER PLANTS, however, won't fix Dabo Guan,a climate change economist at r the Glass City's millions of square meters the University of East Anglia in Norwich, i of heat-leaking windows and buildings that U.K. "It doesn't help, it's actually worse;' pop up like burning candles on thermal Guan says. images. "Hands down, the existing glass Most of the choices that determine a towers downtown are going to be the big city's environmental footprint lie beyond Best challenge,"says Sean Pander,manager the reach of planners, says Jennie Moore, of Vancouver's green building program. an urban sustainability expert at the Brit- ; -:,_ "Glass curtain-wall buildings are terrible" ish Columbia Institute of Technology,Bum- and expensive to retrofit, he says. "We've aby. Moore and colleagues calculated that got a lot of them." Vancouver requires a land area of some Some of the older buildings will be torn 2.3 million hectares,about 212 times greater down and replaced by midcentury.And of- than the city itself,to produce the food,en- ficials have steadilytightened efficient er g y gy, and materials it consumes each year. rules for new construction, heading to If Vancouver wants to become truly green, Ml ward the 2030 zero-emissions standards. she estimates it will need to shrink its foot- What will happen to the remaining older print by at least two-thirds. And only its a buildings, however, remains unclear. The residents can make that happen. City Council has adopted an energy retro- Choices made by the city government ac- `'`' fit�z strategy that aims to identify the leaki- count for just 40%of Vancouver's footprint, ' est,least-efficient buildings and offer small Moore found; the remaining 60% is de- incentive payments to support voluntary termined by how residents choose to live, improvements. But it left it to city staff to move around the city, and eat. Consuming work out how to handle the massive costs red meat,for instance, dramatically boosts 110 or the disruption of relocating occupants. a person's footprint because of the land,wa- ter, and energy required for livestock. Her Barber manages this unusual plant, ENERGY-WASTING BUILDINGS are just best guess of what a sustainable Vancouver which is designed to capture the heat and one obstacle standing between Vancouver would look like: Everyone would live in a 1 use it to help supply hot water to 6000 and its lofty goals.Although its mass tran- small, efficient home of about 46 square residences, including the condominiums sit system is bursting,for instance,last year meters per person, eat a vegetarian diet, built for the 2010 Winter Olympic Games, voters rejected raising a sales tax to pay for and get around on non-fossil-fuel-based and some commercial buildings. A mix of improvements, meaning ridership is un- transportation. Moore and colleagues sewage,hot shower water,and other waste- likely to grow further. have reduced this to a laugh line: "closet- water flows through a labyrinth of painted Local voters and City Hall have little say, dwelling vegans on bikes." !' pipes in meticulously clean rooms that feed meanwhile, in other decisions that could an enormous heat exchanger bigger than have a major impact on the city's environ- SrrnNG in his City Hall office, Mayor a semi-trailer truck. The harvested heat is mental footprint. National and provincial Robertson—who bikes to work and keeps returned to the buildings via separate pipes officials will decide whether energy compa- a nearly vegetarian diet(no dairy,but sea- that carry water heated to 65°C-950C. (On nies can build a proposed oil pipeline and food)—acknowledges that Vancouver's goal cold days, natural gas boilers add extra natural gas export facility near Vancouver's is "big, audacious." And he concedes that heat.) The cooled sewage goes to a treat- port, which could dramatically increase as the city has picked off the lower hang- ment plant,and then the ocean. greenhouse gas emissions from shipping ing fruit, "the gains get tougher as we get The plant, modeled after a facility in operations.And as much as the city would greener." Yet he remains undeterred—and Oslo, was more expensive to build than a prefer nothing but zero-emission vehicles he thinks the struggle will position Van- conventional power plant but is far cheaper on its streets,fuel and emissions standards couver to compete in the new economy of to operate, Barber said. And city officials are in the hands of the provincial and fed- an urbanized world."Many cities recognize say encouraging the construction of more eral governments. Provincial rules have the huge economic upside, being branded waste-to-heat plants will be key to reaching even limited the city's ability to combat strongly with green and renewable,"he says. their goal of cutting overall greenhouse gas the loss of trees:A$10,000 provincial cap Even as Vancouver becomes more ef- emissions by 80% by 2050. So far, they've on fines for tree removal means regulators ficient, he noted, it remains the fastest achieved a 7%cut. have little leverage to deter affluent land- growing metropolitan economy in Canada. Other sources of renewable energy will owners from deforesting for a better view. "People want to be here," Robertson says, drive further progress.The city has adopted Such issues highlight a broader chal- "and work in low-carbon industries and live policies designed to help utilities cover the lenge,analysts say:making sure city efforts in a multicultural, cosmopolitan city where heftier up-front cost of clean energy sys- mesh with national and international poli- they don't need to own a car"m tems by spreading it across many buildings cies. A cautionary example arose during and many years. One proposed project, for a recent meeting in Paris of the C40 Cit- Kenneth R. Weiss,who won the 2007 example,will enable a utility that provides ies Climate Leadership Group, made up Pulitzer Prize for Explanatory Reporting, heat to more than 210 of the largest down- of cities that have set ambitious climate is a journalist in California. SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 921 SPECIAL SECTION URBAN PLANET REVIEW solar energy has dropped by as much as 50%O. Despite substantial economic progress and anti- cipated cost parity with fossil fuels,renewable City-integrated renewable energy for energy technologies have often been criticized for their low power densities, making them urban sustainability inappropriate for urban applications.Conserva- tive estimates of the power density of solar pho- tovoltaies are around 10 W/m2(8),assuming an Daniel M.Kannnen1,2,3*and Deborah A.Sunterl°3 average direct solar irradiation of 100 W/m2, which is typical for the United Kingdom,and a To prepare for an urban influx of 2.5 billion people by 2050,it is critical to create cities that are low- photovoltaic efficiency of 10%. However, the carbon,resilient,and livable.Cities not only contribute to global climate change by emitting the solar resource is highly region-dependent and in majority of anthropogenic greenhouse gases but also are particularly vulnerable to the effects some regions,annual direct solar irradiation can of climate change and extreme weather.We explore options for establishing sustainable energy exceed 300 W/m2 (9).Many of the regions ex- systems by reducing energy consumption,particularly in the buildings and transportation sectors, pected to experience the greatest increase in and providing robust,decentralized,and renewable energy sources.Through technical urbanization are located in solar-rich regions. advancements in power density,city-integrated renewable energy will be better suited to satisfy For example,the majority ofthe total land area the high-energy demands of growing urban areas.Several economic,technical,behavioral,and of India experiences an annual direct solar ir- political challenges need to be overcome for innovation to improve urban sustainability. radiation of over 200 W/m2(10).Additionally,the efficiency of photovoltaics has increased steadily ince 2007,a greater percentage ofthe glob- portunities exist,but focusing on city-integrated and has already surpassed 40%in the laboratory, al population has been living in urban areas renewable energy—defined as distributed,non- using concentrated multijunction cells(11).Hence, than in rural areas.Increased urbanization fossil fuel energy generated locally in urban under optimal conditions,the power density of is expected to continue,with two-thirds of areas—has the potential to help cities meet several photovoltaics could exceed 120 W/m2. the world's population projected to live in sustainability needs.Many of these renewable Several studies have estimated the photovoltaic urban areas by 2050,a net urban influx of 2.5 sources increase regional energy independence potential of existing cities.City-integrated photo- billion people(1).Cities today are generally not and can be redundant with other sources,thus voltaics have the potential to satisfy 62%of the equipped to address dramatic urban growth and increasing resiliency.Although there are several current electricity needs of Oeiras,Portugal(12), strain on existing infrastructure in a sustainable existing barriers to their adoption,solutions will and 66% of the electricity needs of Bardejov, way,especiallywith respect to their energy systems. involve increased power densities of renewable Slovakia(13).High-efficiency commercially avail- To be sustainable,cities must themselves,or in energy technologies,improved infrastructure ca- able photovoltaics only on suitable rooftops could the resources that they command,become low pable of supporting widespread integrated energy satisfy 19.7to 31.1%ofthe daily electricity demand carbon,resilient,and livable(2).Although there generation systems,and increased urban energy and 47.7 to 94.1%of the morning peak electricity can be considerable variation in methods for eval- efficiency,particularly in the buildings sector. demand of Mumbai,India(10).With a 20%adop- uating the emissions footprint of cities(3),with tion rate,solar-powered urban microgiids could 54%of the population living in urban areas,it is City-integrated renewable energy reduce the grid demand in Cambridge,MA,to estimated that cities are currently responsible for About 75%of power generated globally is con- almost zero at midday(14). 60 to 70%of anthropogenic greenhouse gas emis- sumed in cities (5). Generating city-integrated Heating accounts for 40 to 50%of the global sions(4).The two main strategies for transition- energy at the site of energy use could substan- energy demand and 75%of the energy demand ing to a low-carbon city are to shift from fossil tially contribute to the environmental,economic, within the buildings sector(15).Urban solar ther- fuels to cleaner energy sources and to reduce ur- and social aspects of urban sustainability.Four mal energy,specifically for space and domestic ban energy consumption levels.The low-carbon characteristic advantages of such distributed en- water heating,has been an area of particular re- transition can be accomplished through energy- ergy systems include the ability to(i)offer low to search interest.With efficiencies up to 80%(15), efficiency measures,behavioral interventions,and zero carbon emissions,(R)offset capital-intensive solar hot-water systems offer a thermal power incorporating carbon sinks such as urban parks. investments for network upgrades,(iii)impart densityup to 24fl W,/m2 under optimal conditions Cities and their energy systems should also be local energy independence and network security, (Wt,watt-thermal),whereas the global averaged resilient to natural and human-made threats(2). and(iv)motivate social capital and cohesion(6). thermal power density of solar heat collectors is The energy systems of cities are increasingly vul- With limited available installation space, re- 67 Wt/m2(16).Because domestic solar hot-water nerable to the effects of climate change and ex- newable energy generation within urban areas heaters are low-cost and compact, one study treme weather,including storms,flooding,and poses particular challenges.We use the balance showed that 84%of urban households in China sea-level rise, and also to natural and human- between the high energy demand of cities and the could install the system on their rooftops Q1 ). induced disasters.In addition,urban energy sys- available energy density supplied by renewable Solar thermal energy is also used for passive and tems directly affect the well-being and happiness sources as a starting point for an analytic frame- active space heating.A study of five Australian of urban inhabitants.Health conditions,economic work for decarbonized urban spaces(Mg.1).How- cities showed that the use of a Ti ombe wall could competitiveness,cultural appeal,and social,gen- ever,in the waves of innovation that will be needed, offer energy savings up to 17%(18).Seasonal solar der,and racial equality are influencedbyhigh-energy strategies ranging from space-based solar energy thermal energy storage is an approach that stores sectors such as transportation,food production, to small modular nuclear power systems, deep solar thermal energy collected in the summer for and water quality. geothermal systems,and other generation options heating in the colder months. This technology Here we evaluate some of the more promising could transform the energy landscape.In addition provides up to 91%of the total energy needs of a recent technological advancements that could help to reducing greenhouse gas emissions,these strat- large residential building in Richmond,VA(19). urban areas become sustainable cities.Many op- egies may reduce the consumption of water,air, The exploitability of the solar resource is high- and other resources. ly affected by urban form.Although taller build- 'Energy and Resources Group,University of California, ings offer higher surface-to-volume ratios,allowing Berkeley,CA,USA. ZGoldman School of Public Policy, Solar energy for increased facade-integrated solar technologies, University of California,Berkeley,CA,USA.3Renewable and Recent economic and technical advances have they also increase the risk of vertical obstruction Appropriate Energy Laboratory,University of California,Berkeley,CA,USA. made city-integrated solar technologies increas- and shading(20).Although building facades pro- *Corresponding author.Email:kammen@berkeley.edu ingly attractive.Since 2010,the installed price of vide almost triple the area of building roofs,they 922 20 MAY 2016 VOL 352 ISSUE 6288 sciencemag.org SCIENCE f received only 41%of the total irradiation in Karl- has an electrical power density of 283 W/m2(23), trical power density of a geothermal power plant sruhe,Germany(21).However,an optimized urban but some plants are estimated to have a total is estimated to be 50 to 80 W/m2(16).Geother- form could increase the solar irradiation on fa- power density of nearly 800 W/m2(16).Geother- mal energy is more efficiently extracted as heat. caries by up to 45%in greater London,whereas an mat plants can be placed on multiple-use lands, Iceland's Hellisheidi combined heat and power increase of only 9%is possible for rooftops(22). sharing space with activities such as farming and plant is able to generate hot water at 25,000 We skiing. However, the surrounding land can be (I6). Most cities, however, are located in areas Geothermal energy affected by subsidence,erosion,landslides,and with far fewer geothermal resources.Convention- Geothermal energy has been harnessed for both induced seismicity(16,23).When taking into al geothermal resources would only produce a electricity and heat.A typical geothermal plant account all such affected areas,the typical elec- mere 0.017 W/m2 of electricity in the United King- dom(8),but deep(>10 km)geothermalpower could I 103 transform this baseload resource into a far more S°iarh 0 80/, Ot A substantial(>10%)element of urban energy supply f deep enhanced geother- wwater Bj�hP� water 240 (24).The power density WhPrm mat systems is betweeno0.59 and 1.19 WW/mde ==a o dr�rna ai�ni2 pending on the available resource temperature(25). o �rC o °(arI ""•..,, Although the use of geothermal energy for elec- ' �` trical en 102 ® e "'•. iY generation in cities is limited,more than c ®�W e G°°them ' •., 60 countries are using geothermal energy for household, , d in 4 Cstrial heat(16). °other�a�CC matt The thermal powerrcial densities in most regions are 4ohelh viz relatively high,even at moderate depths.In the ._ na(VA T niz United States,the average thermal power density heat 101 Cr �dfrrij�117Gy a <-Wa 30 of hor- izontal closed ed ground-source ops buriedjust 1 to 2 m deeps is 40 Wtlm�for 100 Wr/m2 for boreholes at least 150 in deep(16). Ground-source heat pumps for Cr° �na(Nq heating aSt°41/yam v` ng in Chinese urban buildings could educe en- ergy consumption by 10 to 15%in civil buildings �z and 25 to 30%in public buildings(26).Ground- source heat pumps could also meet the heating 103 demands of 58 to 70% of buildings in West- minster,London,and,if a well-organized district ro heating system was used, all heating demands c was 7, could be satisfied throughout the urban area(27). to IYimz Urban areas may be particularly well suited for ground-source heat pumps because of the ur- S- 102 waste ban heat-island effect,a phenomenon in which +° a lyi�a human activities cause cities and metropolitan areas to be warmer than their surrounding rural increased hropogenic a o o© ©er uxes n ' ) w�4d(Vgll,�s).3 into the subsurface of a e city result ne eat v ed o e C iYi�? groundwater temperutures,enhancing the geother- 41)� 101 Cho As, 5 yi �r0ps 1°�;- mal resource.In Karlsruhe and Cologne,Germany, „t n�z the anthropogenic heat fluxes could sustainably provide 32 and 9%of the annual residential space T ° kind heating needs,respectively(28).The anthropo- m (hgiyTs genic influence on the subsurface temperature is o h2 ~ 100 greater inmegacities such as Shanghai,where the existing heat content in the urban aquifer is 22 103 101 105 times the annual heating demand of the city(29). Population density(people/km2) Wind energy Region Population Urban wind energy provides opportunities for ASIA r3 LAC ;;.I MAF —0ECD90 ENREF •Q million •10 million 020million 030million not only renewable electrical generation but also ventilation,pollution dispersion,and mitigation Fig.1.City-integrated renewable energy potential.(A)Potential for renewable sources to satisfy total of the urban heat-island effect Urban wind energy final urban energy consumption and (B) urban transportation energy demands. Solid lines represent has not been widely adopted,largely because of typical performance. Dotted lines represent potential performance, based on optimal conditions and challenges and concerns related to installation technologies currently available in the laboratory.All resources are evaluated based on electric power space,low and turbulent urban wind-speed char- densities, except geothermal energy and solar hot water. Geothermal energy is evaluated based on acteristics,vibration,noise,safety,shadow flicker thermal power densities for horizontal closed loops buried 1 to 2 m deep at the low end and boreholes at (periodic shadows cast by the rotating blades of least 150 m deep at the high end.Data on total final energy consumption and region definitions are from wind turbines),and aesthetics(30).Although mod- (77),city population size and density data are from(78),and transportation data are from(79)."Waste" ern wind farms typically produce 2 to 3 W/m2 with refers to LFGTE.PV,photovoltaics.Population is indicated by circle sizes,and regions are indicated by circle horizontal-axis wind turbines(HAWTs), counter- colors(ASIA,Asia excluding OEDC90 countries;LAC,Latin America and the Caribbean;MAF,the Middle rotating vertical-axis wind turbines(VAWTs)can East and Africa;OEDC90,member countries of the Organization for Economic Cooperation and Development achieve 30 W/m2(31).In addition to increased as of 1990;REF,Eastern Europe and the former Soviet Union). power density,VAWTs offer several advantages SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 923 ISPECIAL SECTIONURBAN PLANET that are particularly relevant to the urban envi- creased global urbanization is expected 1500 2.5 ronment These include lower dependence on wind to result in increases in municipal solid Current direction,ability to handle higher turbulence and waste(MSW)(Fig.2).Typical manage- ®Projected 2025 varied wind speeds,lower manufacturing costs, ment strategies include recycling,burn- , and decreased impact on birds and aircraft(30). ing,or,landfilling.Although recycling � 1200 2.0 y Another benefit is that the generator and gearbox can reduce the life-cycle energy,it may o can be installed at ground level,allowing building- not be economically or energetically g mounted turbines to be more easily serviced(30). realistic for some waste. . �I'i 900 1.5 Numerous researchers have investigated urban Energy from waste may be derived 3 v wind-flow characteristics,resulting in estimates from landfill-gas-to-energy(LFGTE)sys- c of its potential for urban electricity generation, terns and waste-to-energy(WTE)plants. Excluding thermal energy needs,urban wind Landfill gas is generated through the i@ 600 1.0 could provide 33%of residential building elec- biological degradation of organic mate- tricity needs with HAWTs in urban areas of New rials in MSW,typically consists of meth- ID 3 Zealand(32)and 40%with VAWTs in San Cataldo, ane (50 to 60%) and carbon dioxide 300 0.5 a Sicily(33).There are limited examples of existing (40 to 50%),and can be collected and a' urban wind projects.In Bahrain,the World Trade burned to generate energy.The aver- Center twin towers use three vertically arranged age LFGTE power density that could HAWTs, providing 11 to 15% of the electrical be extracted from this gas is estimated 0 �"°I � 0.0 energy needs (30).Although the two VAWTs to be 4.1 W/m2,but, if optimized, a ASIA LAC MAF OEDC90 REF installed at the Pearl River Tower in Guangzhou, theoretical power density of 10 W/m2 China,provide only 5%of its energy needs(30), is feasible(39).In a WTE plant,MSW Fig.2. Estimates of current and projected generation of they offer several design advantages.The curved is incinerated, generating 0.6 MWh urban waste.The amount of MSW that is generated daily glass facade of the building funnels air to the per ton of MSW on average (MWh, (solid bars)and the projected daily waste production by 2025 VAWTs at speeds of 1.5 to 2.5 times the ambient megawatt-hour),with the potential to (striped bars) in each region are indicated on the right axis wind speed,allowing the turbines to generate generate up to 1.8 MWh per ton(40). [data are from(38)].If all urban waste were to be burned in 15 times more energy than freestanding wind Additionally, many WTE plants use WTE plants, the corresponding energy that would be gen- turbines could(34).Additionally,byallowingwind cogeneration,providing useful heat.If erated,based on an average waste energy value from(40) to pass through the building,wind-induced forces all ofthe MSW generated in the United that includes nonrecyclable plastics,is indicated on the left axis. on the building are reduced, which in turn States in 2011 was sent to WTE plants, reduce the quantity of steel and concrete needed enough energy would be produced to power and energy technologies to meet the remaining mini- to maintain the building's stability(34). heat 12 and 8%of American households,respec- mal energy needs(46). tively(40).Additionally,carbon-capture systems Retrofitting existing buildings saves embodied Biomass energy can be integrated into WTE plants,reducing car- energy, avoids generating waste from building Power densities for biomass energy are highly de- bon dioxide emissions by an estimated 90%(41). demolition,and is often more cost-effective than pendent on the regional climate,because it affects constructing newbuildings.Despite these advan- O Opportunities for reducing which plants are able to grow locally. Conven- pp g tages,the rate at which the current building tional crops have a range of power densities from energy consumption stock is retrofitted is startlingly slow.In the United roughly 0.05 to 1.7 W/m2;the highest densities Two major sectors for reducing energy consump- States,the existing commercial building stock is come from crops grown in tropical locations with tion are buildings and transportation.To limit being retrofitted at a rate of roughly 2.2%a year; genetic modification,fertilizer,and irrigation(8). global climate change to 2°C above preindustrial with the median energy savings from these re- The ongoing debate over biofuel sustainability levels,the greatest global investment is required trofits at roughly 11%per building(4�).Most of and social and environmental justice consider- in the buildings sector(an estimated incremental these retrofits consist of minimally invasive mea- ations places this potential energy source in a com- expenditure of$300 billion/year for 2015-2020) sures with short payback periods,such as lighting plex and unsatisfactory position.Direct combustion for both retrofitting and constructing new build- and HVAC(heating,ventilation, and air condi- of urban biomass offers at least a clearer life-cycle ings to high energy-efficiency standards(42).The tioning system)replacements.Integrated energy- path to evaluate than conversion and use of bio- next largest investment is required for transpor- efficiency measures are needed to reach savings as mass as biofuels.If short-rotation poplar was grown tation vehicles,with an estimated additional ex- high as 50%(48).These measures include upgrades on marginal lands in Boston,for example,it could penditure of$70 billion/year(42). to the building envelope,mechanical systems,light satisfy 0.6% of the yearly primary energy de- ing and electrical systems,and system controls, mand in Massachusetts(35). Building efficiency improvements as well as changes in tenant behavior(48). Given the low power densities,urban agdeul- Buildings account for 40%of the worlws energy ture may be better suited for food than for en- consumption and 30%of annual greenhouse gas Transportation ergy.Urban farms help reduce urban heat-island emissions(43).To accommodate the growing ur- The five potential metrics for the decarboniza- effects,mitigate urban stormwater impacts,and ban population,new buildings are needed.Eighty tion of urban transportation are(i)fuel carbon lower the energy needed for food transportation percent of all buildings that will stand in India in intensity,(H)energy intensity,(iii)vehicle occu- (36).A life-cycle analysis of a community farm in 2030 had yet to be constructed as of 2010(44). pancy rate,(iv)trip distance,and(v)the number South London has shown that urban food supply This new construction creates opportunities not of motorized trips(49).These metrics are each systems can achieve reductions in greenhouse only for energy-efficient and climate-resilient discussed below. gas emissions that are potentially larger than buildings but also for local optimization of urban those of parks and urban forests(M). form.New buildings could be made 70%more Fuel carbon intensity efficient than existing buildings through the use Fuel carbon intensity is a measure of greenhouse Energy from urban waste of insulated windows,modern gas and oil fur- gas emissions per unit energy. To reduce this Although not entirely renewable,energy from naces, and more efficient air conditioners(45). metric,cleaner energy sources are required and waste could play a key role in sustainable urban Strategies for zero-energy buildings involve mini- may be achieved through fuel substitution or energy.Urban residents produce roughly twice mizing the energy use of abuilding,especially for vehicle electrification.Although fuel substitution the waste of their rural counterparts(38).In- heating and cooling, and adopting renewable with biofuels requires minimal changes to the 924 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE ._...... ......... _ h i i r vehicle and fueling infrastructure and reduces much more common in other areas of the world. economy. In a study of ten megacities, invest- global carbon dioxide emissions when evaluated Globally,37%of trips are nonmotorized,with the ment in climate adaptation was at most 0.33% over the life o cycle of y the fuel tailpipe e carbon di- greatest use P P gr of nonmotorized transport(50%)in of a city's gross domestic product(GDPc)and oxide emissions may be comparable to those pro- the Asia-Pacific region and Africa and the least substantially less in developing countries(62). r duted by fossil fuels(50).To eliminate tailpipe (8%)in North America(58). pollution,vehicles powered by hydrogen or elec- Technical challenges i tricity may be better suited for urban transports- Other factors Some of the main technical challenges for imple- tion.Although roughly 961.of hydrogen production The urban transportation landscape is changing menting city-integrated renewable energy are today uses conventional methods with fossil fuels with increased car-sharing programs and the the uncertainty and variability in urban energy (51), there are numerous emerging low-carbon emergence of self-driving cars. It is still some- use and the methods used to account for the r production methods(52).However,cost and en- what unclear what effect these will have on en- associated emissions(3).Municipal governments ergy storage remain major obstacles.The electri- ergy consumption,because they may result in typically measure emissions using a territorial fication of the transportation sector is expected to increased low-or even no-occupancy motorized approach,primarily counting emissions that en- grow rapidly,with plug-in hybrid vehicles pre- transportation.One model predicts that shared ter the atmosphere within the jurisdiction's geo- j dicted to account for 58%of new light-duty ve- autonomous vehicles could reduce the number graphic boundary(63).There is increasing interest hicle sales in the United States by 2030(53).This of cars in use by a factor of 10,but the total mo- in accounting for emissions on a consumption growth requires improvements in low-cost,com- torized distance traveled would increase by basis, allocating all emissions in global supply pact,long-lasting battery technologies and vehi- 11%(59). chains to the points at which products and ser- cle charging infrastructure. The environmental vices are consumed(64).This approach empha- benefit of electrifying urban transportation will Challenges of dramatic sizes the mitigation potential of households and largely depend on the emissions from the elec- urban decarbonization required energy needs for includes a wider range of emission sources,in- tricity generation.The re q gY cluding transportation,energy,food,goods and transportation could be achieved,or partially Economic challenges services,water,waste,and home construction. achieved,using city-integrated renewable energy Some believe that it is too expensive to invest in Cities differ in both their energy needs and (Fig.1B), dramatic decarbonization; however, it may be their available energy resources. Hot and cold even more expensive not to. Global infrastruc- climates have substantial air conditioning and Energy intensity ture needs for 2015-2020 are 6.7 trillion ear heating $ /y needs,respectively.Cities with more in- Energy intensity is the energy required to move a under business-as-usual scenarios,and the incre- dustrial processes typically consume more energy, vehicle one kilometer. Achievable advances in mental costs of low-carbon infrastructure are on however,they also have increased potential for engine technology can improve the fuel economy the order of-$70 billion/year to $450 billion/ district heating and combined heat and power. of automobiles by over 50%and trucks by over year(60).Although these are global estimates, Urban form also stron gly influences transports- 30%(54).Although such improvements are pos- port cities with populations over 1 million are tion energy needs.Available energy sible,the greatest reduction requires a systems particular) vulnerable to infrastructure e en- cal resources ion Y xp pend on the status of the electrical grid,location approach,taking into account numerous other ditmes related to coastal flooding.Nearly40 million of renewable resources,and socioeconomic con- tactors including vehicle lightweighting,accessory people and$3 trillion of assets are currently ex- ditions.There is considerable variation in energy load management,powertrain systems optimiza- posed to a 1-in-100-years coastal flood event(61). use not only between cities but also between lions,and aerodynamics.Advances in lightweight By the 2070s,the exposed population could grow neighborhoods within the same city.For exam- materials show particular promise:Passenger ve- by a factor of 3 and the value of vulnerable assets ple,average household carbon footprints in the hicle fuel efficiency can be improved by 6 to 8% could increase 10-fold under the combined effects San Francisco Bay Area vary between neighbor- for each 10%reduction in weight(55). of sea-level rise,subsidence,increased urban pop- hoods according to income,vehicle ownership, Vehicle occupancy rate ulations,and economic growth(61).Despite the household size, home size, carbon intensity of global need for climate adaptation,investment electricity production, population density, and Public transportation and carpooling are com- in adaptation is a small part of the overall urban other factors(Fig.4)(65). monly used strategies to increase vehicle occu- pancy rates.A higher urban density increases the attractiveness of public transportation.For rea- awl 100 sonable spatial and temporal availability,the ur- rREASIA Population ban density threshold for public transportation > oLAC <1 million is estimated to be 5,000 people/km2(56).Cities MAF • 10 million with population densities below this threshold N 80 OECD90 020 million are those with the highest percentage of their ® REF 030 million transportation needs being met by private mo- a, torized vehicles(Fig.3). ! 60 Trip distance and number of motorized trips o 40 ; Trip distances and the numbers of trips taken E i per year per person depend on the built envi- o. ronment.A city with high density and mixed-use ,_- 20 development allows for shorter trips that are c more conducive to nonmotorized means,such as walking and biking.The built environment must a 0 include safe infrastructure to facilitate nonmo 0 5 10 15 20 25 30 35 torized transportation.A study of five U.S.cities Population density(thousand people/km2) found that bicycle ridership increased between 21 and 171%within one year of building protected Fig. 3. Relative use of private motorized vehicles. Plotted are the percentages of trips taken using bicycle lanes (57). Bicycle use and walking are private motorized vehicles,relative to urban population densities.Data are from(79). SCIENCE SC1enCCmag.Org 20 MAY 2016•VOL 352 ISSUE 6288 925 SPECIAL SECTION URBAN PLANET Given the uncertainty and variability in urban Opportunity for thermal storage is growing. of electricity fundamentals but also of the eco- energy systems and urbanization dynamics, a Using thermal storage could double the photo- nomic value of energy efficiency and renewable flexible and adaptive solution is necessary.Pobr voltaic capacity of Shanghai, for example (69). energy generation.For example,most businesses visibility,aging infrastructure,and spatially and Although water remains the most widely used remain uninterested in investing in renewable temporally variable energy generation from dis- material for sensible heat storage,other methods, power,because energy generation is outside their tributed renewable energy sources have made such as packed beds and phase change materials, core business goals,despite the increased profit the current electrical grid susceptible to frequent are emerging(70).Thermochemical heat storage margins that these installations could enable. disturbances that can lead to cascading failures. offers the greatest potential energy density and A harmful misconception is that freedom and One solution would be a smart grid with inte- does not suffer from heat losses during storage, social well-being are best achieved through abun- grated energy storage.A smart energy grid should but development efforts are at an early stage. dance and excessive consumption. Often, effi- not be limited to electricity,rather,electricity, ciency improvements are outpaced by increased Behavioral challenges consumption.For example,the floor area of new thermal, and gas grids should be combined P P and coordinated,emphasizing the role of district From the mundane decisions of whether or not single-family detached houses in the United States heating in future sustainable cities(66).Even if a to unplug a cellphone charger or take public has increased so much since 1978 that single- smart gird is well monitored and controlled,the transportation to more momentous decisions family housing uses more energy than multi- high variability of renewable energy resources re- such as installing solar panels on a roof,behavior familyhousing both per household and per person, quires adequate storage.As the prices of batteries shapes how we live our lives and the energy despite the efficiency gains achieved through the go down and their performances improve, dis- choices we make. On an individual level, the enforcement of new building codes (74). Even tributed electrical storage shows potential not effect is minimal,but in aggregate it is substan- WTE programs indirectly encourage increased consumption.Coupled with increased consump- tion is a strong sense of entitlemeM Whereas -? conventional power plants have typically been F located outside of cities and neighborhoods, renewable energy generation is best placed in 's resource-optimal sites and/or close to the end user.Unfortunately,there has been strong resist- ance to this,because many people prefer such e e development to happen elsewhere("not in my ! d3fif',4 backyard").Individuals often find their time and 1 T comfort to be more important than that of others and choose private vehicle use over public trans- . ..,.. portation,leading to increased congestion,delays, p, and inconvenience for the broader community. Not only do individuals need to understand how their behavior affects energy use, society, and the l emissions w m environment but,more importantly,they need Tota t ye` to care. (COze)per houshold 14.3-30.9 ®. e a 30.9-34.7 O Policy challenges a r 34.7-37.8 Although each country suffers its own political ® _ 37.8-40.5 challenges,similarities can be found in the treat- i 40.5-43.4 ment of renewable energy and energy-efficiency =43.4-46.6 measures.The research and development fund- =46.6-49.7 ing in these areas is nonexistent in some countries 49.7-54.2 and undersupported in others,slowing innovation. 54.2-61.4 Global research and development funding in 61.4-103.7 renewable energy fell 3% in 2012 and 2% in Fig.4.Neighborhood variation in household carbon footprints.The map shows the average house- 2013(75). hold carbon footprint of census block groups in selected San Francisco Bay Area cities.The color Subsidies and incentives are often inconsis- gradient indicates deciles from the lowest to the highest carbon footprint. Data are from the model tent. Unlike those for conventional generators, developed in(65)and are available at http://coolclimate.berkekey.edu. policies aimed at encouraging renewable power technologies have changed frequently,discour- aging widespread adoption of the technologies only in standalone units but also in the electric tial.Occupant behavior,for example,can double (73).When incentives are removed abruptly,pro- vehicle fleet.Electric vehicles can provide ancil- the energy consumption of a building(71).Sim- iects can be abandoned before completion and lary services to the grid, such as voltage and ilarly,driving style can influence a vehicle's fuel companies can be bankrupted.Additionally,fre- frequency regulation,peak power leveraging, consumption by up to 20%(72).A lack of infor- quently changing subsidies make it increasingly and reactive power support to enhance the mation,or selfishness,may lead us to make poor difficult to obtain financing for renewable energy operational efficiency,secure the electric grid, energy choices, even when they are not in our projects.In the United States,policy variation be- and reduce power system operating costs(67). individual and collective best interest(73). tween states deters investment,complicates com- Electric vehicles couple well with renewable re- Conventional power generation systems,typi- pliance,discourages interstate cooperation,and sources.For example,installation of photovolta- cally located outside of cities and neighborhoods, encourages tedious and expensive litigation(76). ics in parking lots in Frauenfeld, Switzerland, are out of sight and,therefore,out of the minds An effort to promote renewables has to be sus- could supply 15 to 40%of the future electric ve- of general consumers. This apathy has led to tained,orerly,substantial,predictable,credible, hicle energy demand in that city(68),and urban major misunderstandings.For example,only 12% and ramped(73). electric vehicle strategies in cities in developing of Americans could pass abasic electricity literacy Policy-makers have focused their efforts on countries could particularly benefit the poor. test(73).There is not only a lack of understanding technical challenges. Although there are still 926 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE opportunities for technical improvements, Overcoming challenges to 4. United Nations Human Settlements Programme,Cities and more comprehensive policies are needed to over- dramatic decarbonization Climate Change:Policy Directions(UN,2011). come economic and behavioral challenges.Empha- Economic,technical,behavioral,and policy Chal- 5. D.Dodman,Environ.Urban.21,185-201(2009). fi 6. A.M.Adil,Y.Ko,Renew.Sustain.Energy Rev.57,1025-1037 sis is needed on government efforts to increase lenges have been identified as barriers to dra- (2016). public understanding of energy systems and the matic urban decarbonization.However,there are 7. U.S.Department of Energy,"Solar Power;'in Quadrennial environmental impact of behavioral choices. several immediate actions that can be taken to Technology Review 2015(U.S.Department of Energy,2015), begin to address these: (i) Economically Value chap.4,Technology Assessments. 8 D.J.MacKay,Sustainable Energy-Without the Hot Air UIT An innovation agenda for clean urban environments specifically through Cambridge,2009). urban sustainability the positive environmental justice benefits,and 9. NASA,Surface Meteorology and Solar Energy data set,release Achieving a sustainable urban energy system will use this valuation to invest in disadvantaged com- 6.0(NASA,2014);https://eosveb.larc.nasa.gov/sse/. 10.R.Singh,R.Banerjee,Sol.Energy 115,589-602(2015). require a dramatic rethinking of our infrastrvc munities.(ii)Standardize carbon and water ac r 11. National Renewable Energy Laboratory,"Best Research-Cell ture,information Systems,and critical Social and Counting to improve resource efficiency today and Efficiencies'(National Renewable Energy Laboratory,2015); environmental justice issues.We pose here a enable atransition t0 resource and pollution mar- m"v.nrel.gov/ncpv/images/efficiency-chart.jpg. number Of immediate opportunities t0"green" kets over time.(iii)Mix fee-bates(fees associated 12. M.Amado,F.Poggi,Energy Procedia 48,1539-1548(2014). the process of urban evolution,as well as pres- with polluting vehicles that finance clean vehicle 13.J.Hofierka,J.Kailuk,Renew.Energy 34,2206-2214(2009). 14. A.Halu,A.Scala,A.Khiyami,M.C.GonzSlez,Sci.Adv.2, sing research questions for sustainable cities,both purchases) and congestion pricing to improve e1500700(2016). theoretical and practical.We recommend analysis urban air quality and reclaim city centers for 15. Z.Wang,W.Yang,F.Qiu,X.Zhang,X.Zhao,Renew.Sustain. and practice to reach sustainability goals,accom- pedestrians and social spaces. Meanwhile, the Energy Rev.41,68-84(2015). anied b a new suite of data-intensive metrics on following 16.V.Smil,Power Density.,A Key to Understanding Energy Sources p y g pressing research questions remain, and Uses(The MIT Press,2015). which to base planning decisions. Can urbanization in emerging economies be- 17. H.Wei,J.Liu,B.Yang,Appl,Energy 126,47-55(2014). Renewable generation and reductions come a force for sustainability and equality?The 18.C.Castelldn,A.Castell,M.Medrano,I.Martorell,L.F.Cabeza, g unprecedented growth in population and resource J.Sol.Energy Eng.131,041006(2009). in consumption demands in large Asian cities has made the urban 19. L.T.Terziotti,M.L.Sweet,J.T.McLeskey Jr.,Energy Build.45, 28-31(2012). Although city-to-city and regional variations are environment more polluted and more of a re- 20.S.Freitas,C.Catita,P.Redweik,M.C.Brito,Renew.Sustain. important to consider, many city governments source drain than any other demographic trend Energy Rev.41,915-931(2015). could immediately(i)encourage energy storage over the past four decades.Resource allocation, 21. K.Fath et al.,Sol.Energy 116,357-370(2015). and low-carbon generation at the building level combined with a new focus on quality of life, 22.J.J.Sarralde,D.J.Quinn,D.Wiesmann,K.Steemers,Renew. Energy 73,10-17(2015). through smart net-metered urban distribution should become a means to reverse the trends that 23.A.Kagel,D.Bates,K.Gawell,A Guide to Geothermal Energy networks; (ii) reclassify electric vehicles as ap- have swept Asia These development trends will and the Environment(Geothermal Energy Association,2007). pliances,so that electric vehicle purchases could ultimately be played out in Africa and elsewhere. 24•T.J.Reber,K.F.Beckers,J.W.Tester,Energy Policy 70,30-44 be amortized into building capital budgets;and Howwill we give environmental justice a more (2014). 25,A.Lopez,B.Roberts,D.Heimiller,N.Blair,G.Porro,U.S. (iii) provide intra-city and city-suburban mass central role?Arguably the most central issue in Renewable Energy Technical Potentials:A GIS-Based Approach transit in the cleanest and most inclusive forms urban sustainability is whether city management (Technical Report NREL/TP-6A20-51946,National Renewable possible.In the near term,the following research can move to a paradigm where environmental Energy Laboratory,2012). questions should be addressed. justice is not an occasional response to crises of 26.J.Zhu of al.,Energy 93,466-483(2015). 27.Y.Zhang,K.Soga,R.Choudhary,G€otech.Lett.4,125-131 Can networked smart buildings themselves inequality but one where we reap the benefits of (2014). become the building blocks of a low-carbon city? proactive and inclusive planning, design, and 28.S.A.Benz,P.Bayer,K.Menberg,S.Jung,P.Blum,Set.Total Buildings that are designed to create clean en- operation.It is important that renewable energy Environ.524-525,427-439(2015). ergy,store excess generation,and feed this stored generation,improved energy-efficiency technol- 29.K.Zhu,P.Blum,G.Ferguson,K.-D.Balke,P.Bayer,Environ. Res.Lett.5,044002(2010). energy back into the regional matrix when de- ogies,and low-carbon transportation are widely 30.T.F.Ishugah,Y.Li,R.Z.Wang,J.K.Kiplagat,Renew.Sustain. mand or prices warrant would be key elements accessible,particularly to low-income populations Energy Rea 37,613-626(2014). of an energy-smart network, that typically lack ownership of their residential 31.J.0.Dabiri,J.Renew.Sustain.Energy 3,043104(2011). Do cities have an optimal size or density?Ur- buildings and have the longest commutes. Im 32.N.Mithraratne,Energy Build.41,1013-1018(2009). 33.A.Gagliano,F.Nocera,F.Patania,A.Capizzi,Int.J.Energy ban infrastructure exists at scales that are im- provements in walkability,urban parks,and air Environ.Eng.4r43(2013). mediate interms ofbuildings andtransportation quality should make cities more livable for all 34.M.A.Kamal,S.Saraswat,Cie Eng.Archie 2,116-120(2014). embarkation-disembarkation points but also inhabitants. 35.M.Saba,M.J.Eckelman,Appl.Energy 159,540-547(2015). complex and decentralized in terms of networks Ultimately, these and other questions will 36.K.Ackerman et al.,Econ.Sec.Rev.45,189-206(2014). that supply food and water to the formal city require a new coordination of technical,social, 37.M.Kulak,A.Graves,J.Chatterton,Landsc.Urban Plan.111, 68-78(2013). center and suburbs.Many services that are seen behavioral,and market innovations.Cities planned 38.D.Hoomweg,P.Bhada-Tata,What a Waste:A Global Review of as "citywide" may, in fact, be better suited to around resource demands,or personal automo- Solid Waste Management(World Bank,2012). regional distribution or even remote management biles,have been tried and ultimately found lack- 39.H.R.Amini,D.R.Reinhart,Waste Manag.31,2020-2026 The trend toward megacities,particularly in Asia, ing in their ability to create sustainable spaces.A (2011). presents opportunities for improvements to infra- wave of innovations in physical form,function, 40.N.J.Municipal Soli C.Waste (M e,2014 Energy and Economic Value of Municipal Solid Waste(MSW),including Non-Recycled Plastics structure,such as mass transit,and livable high- and ideally justice and equity offers a new path (NRP),Currently Landfilled in the Fifty States(Columbia density housing.At the same time,walkability toward low-carbon sustainable cities.The chal- University Earth Engineering Center,2014); and quality of life, as well as the potential for lenge is to accelerate innovation and deployment wNvw.americanchemistry.com/Policy/Energy/Energy- Recove ry/2014-U pdate-of-Potentia I-for-Energy-Recovery-from- reduced carbon emissions,are all degraded if ur- so that cities can substantially reduce greenhouse Municipal-Solid-Waste and Non Recycled Plastics.pdf. banism forces the mass movement of people,goods, gas emissions in ways that make them more livable 41.A.Scott,Chem.Eng.News 94,18(2016). water,and energy.Similarly,although increased and equitable,not less So. 42.International Energy Agency,Energy Technology Perspectives population density may reduce transportation 2012:Pathways to a Clean Energy System(International Energy energy use,the resulting increased power density Agency,2012). 43,United Nations Environment Programme,Sustainable Buildings demand may not be appropriately met by city- REFERENCES AND NOTES and Climate Initiative,Buildings and Climate Change:Summary for integrated renewable energy,unless multiple sources 1. 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Change 10.1038/nclimate2944(2016). cycle adequately(2).Urban water management In the process of urban water use,waste is 63.W.K.Fong of al.,Global Protocol for Community-Scale Greenhouse Gas Emission Inventories:An Accounting (UWM)has recently gained more attention, in produced in the form of wastewater.However, and Reporting Standard for Cities(Greenhouse Gas Protocol, part due to the comprehensive Sustainable Devel- wastewater also contains important resources, 2014). opment Goal on Water(SDG-6)(3).The generally including water,organic matter,heat,and nutri- 64.C.M.Jones,D.M.Kammen,Environ.Sci.Technot 45, accepted approach to UWM builds on a well- ents such as phosphorus and nitrogen(Table 1). 4088-4095(2011), established socio-technical system that,at least For example,the amount of nitrogen passing 65.C.Jones,D.M.Kammen,Environ,Sci.Technol.48,895-902 (2014). in the more affluent part of the world,has solved through the human metabolism on a global scale (2 66.H.Lund of al.,Energy 68,1-11(2014). most of the water and hygiene-related problems and therefore potentially ending up in wastewater 67.F.Mwasilu,J.J.Justo,E.K.Kim,T.D.Do,J.W.Jung,Renew. afflicting cities at the turn of the 20th century.The is on apar with major components ofthe nitrogen Sustain.Energy Rev.34,501-516(2014). core centralized services are the'provision of safe cycle.For a population of 9 billion,nitrogen in 68.H.-M.Neumann,D.Scher,F.Baumgartner,Prog.Photovolt. 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N.Baker,K.Steemers,Energy and Environment in Architecture: UWM in high-income countries a"safe operating Space"of humanity(9).In view A Technical Design Guide(E&FN Spon,2000). 72.J.Gonder,M.Earleywine,W.Sparks,SAE Int J.Passeng,Cars The UWM system relies on investment intensive, of the large losses of nitrogen in agricultural pro Electron.Electr.Syst,5 450-461(2012). usually underground,pipe networks that provide duction(10),the world can only be kept within 73.B.K.Sovacool,Energy Policy 37,4500-4513(2009). single-quality drinking water and evacuate storm- the suggested boundary with a dramatic increase 74.Y.Ko,J.Plann.Lit.28,327-351(2013). 75.Frankfurt School-United Nations Environment Programme water and wastewater.In many places,reservoirs in nitrogen recycling from wastewater. Centre,Bloomberg New Energy Finance,Global Trends in and long-distance water conveyance systems com- The current UWM approach has worked so Renewable Energy Investment 2014(Frankfurt School of pensate for inadequate local water resources.In well because it delivers its main services securely Finance and Management,2014);http://fs-unep-centre.org/ addition,water and wastewater treatment plants at a good quality to a majority ofpeople in a region. system/files ol,C.l Cooper, Electr J.2 , provide an interface to the aquatic environment, Its institutional side is characterized by planning 76.B.K.Sovacool,C.Cooper,Electr.J.20,48-61(2007). 77.Global Energy Assessment,Global Energy Assessment-Toward treating raw water for drinking-water purposes and investment processes traditionally delegated a Sustainable Future(Cambridge Univ.Press and the and wastewater for water pollution control.In- to municipal water authorities.These actors follow International Institute for Applied Systems Analysis, deed,the main components of the UWM system well-formulated regulatory codes in their opera- 2012). have been considered the most important med- tions and rely primarily on highly specialized 78.Demographia,Demographia World Urban Areas:11th Annual Edition(Demographia,2015). ical advance since 1840(5)and still serve as the technical expertise. 79.International Association of Public Transport(UITP),Millennium prevailing model for prospering cities worldwide The downsides of the current UWM system Cities Database for Sustainable Mobility(UITP,2001). (g),An additional important infrastructure-besides are its strong dependence on large quantities of ACKNOWLEDGMENTS water Supply and Wastewater removal and water(Fig.1),high investment costs,and a need We thank F.Creutzig,C.Jones,B.Gould,J.Sager,J.Apte,and treatment-is the stormwater drainage system, for stable institutions,as well as long planning D.Lemoine for useful discussions.This research was supported by On a local level,the built environment has a horizons and inefficient use of resources..Whereas the Karsten Family Foundation and the Zaffaroni Foundation most of these disadvantages have different im- through their support of the Renewable and Appropriate Energy iEawag,Swiss Federal Institute of Aquatic Science and plications depending on the context,inefficient Laboratory(to D.M.K.)and by an Energy Efficiency and Renewable 2 Technology,8600 Dobendorf,Switzerland. Faculty of use of resources is agloballssue.Despite thehigh Energy Postdoctoral Research Award from the U.S.Department of Geosciences,University of Utrecht,Heidelberglaan 2,NL- amounts of energy in wastewater able 1)'waste- Energy(to D.A.S.). 3584 CS,Utrecht,Netherlands.3Institute of Environmental Engineering,ETH Zurich,8093 Zurich,Switzerland. water management is a net consumer of energy, 10.1126/science.aad9302 *Corresponding author.Email:tove.larsen@eawag.ch and recycling of nitrogen is only possible to a Very 928 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE I r I small degree within the existing system(11).Ad- ditionally,the substantial investments inmfiastrLic Table 1.Resources in wastewater.For nutrients and water,global averages are given. No global in- ture required to move the large amounts of water formation is available concerning warm water and organic matter in wastewater. Local loads depend in and out of cities and treating the resulting waste- inter aria on nutritional status,household devices,water availability,and habits. water are of interest beyond the local setting.The most transparent report from the Organization for Economic Cooperation and Development(OECD) Water(liters person-1 day-') .......................................................................................................................................................................................I....................... (12)calculates a global investment need of US$772 Domestic 184 Global average(69) .......... .................................................................................................................................................... ...... ........................ billion year-1(or about 19/6 of gross domestic product) Industrial 300 Industrial global average(69) .......................................................................................................................................................................................... by 2015 far the OECD countries and Brazil,Russia, Energy(MJ person'year 1) I` ..................................................................................................................................................................................................................... India,and China However,other literature estimates Heat contained in warm water 2800 Typical European country(11) I .............. .......................................................... are highly variable,from US$190 billion year'to Chemical energy contained in organic matter 540 Typical European country(11) US$1037 billion year'(13,14).Additional US$114 .............................................................................................................................................................................................. Chemical energy"embedded"in N and P 180 Global average,year 2000(11,17) billion ear'[US$71 billion to US 166 billion year 1 ..........................................*e-t-.,b-o",..............................._1........_ ................................................................................................... r Y $ y Nutrients from human metabolism(g person day) .......................................................................................... ... (15)]are required to achieve universal access to safe Global average,Nitrogen(N) 10 Global average,year 2000(17) drinking water and adequate sanitation for all by Phosphorus(P) 2 Global average(17) 2030. Assuming that the investments for water supply and wastewater management are similar in magnitude,the total water infiastluctuie value for a connected global population of 9 billion people rest of the world is certainly riddled with major areas with a low HDI and low institutional reli would amount to about US$60 trillion(16). problems.Although reliable information on sew ability(21).In combination with high discount Today,UWM is incurring increasing economic, ers(Fig.2A)and treatment plants is scarce for rates,indicating a strong preference for spending social,and environmental costs,even in countries Africa and Asia,there is general agreement that money on immediate benefits rather than on with a long tradition of successful practices.This connection rates remain veiy low[an estimated long-term investments(22),there is little willing- is a consequence of (i q aging built infrastructures connection rate of 14%for Africa and 18%for ness and ability to embark on infra- increasing urbanization,emerging contaminants, Asia in 2000(17)],and the overall treatment of structure projects.A modeling study based on competitive water uses,and measures to mitigate the collected wastewater remains highly insuffi- past investment patterns (17) estimated that the effects of climate change(e.g.,water-saving cient,even in capital cities(18).For Latin America, even on the most optimistic assumptions,only measures).Furthermore,public utilities have of- connection rates are higher,but only 15%of mu- 369/6 of the African population and 44%of the ten missed out on charging full-cost tariffs and nicipal wastewaters are treated(19). Asian population will be connected to a sewer are increasingly confronted with a backlog of in- This backlog is compounded with the current network by 2050.The implementation of well- vestments(13).These recent developments ques- unprecedented global population growth rate.A functioning,nutrient-eliminating wastewater treat- tion whether and in what form the existing UWM major part of this growth is projected to take ment plants depends on the previous construction system can still be the best solution for the world place in the cities of Africa and Asia,including of sewers and often involves substantial delays.A as it has been since the beginning of the 20th many countries with a low human development case in point illustrating the enormous resources century(13). index(HDI)as well as pronounced and increas- and sector investments needed has become appar- ing water scarcity(Fig.2B).Small and medium- ent with the Swacbh Bharat national campaign by Limitations for the global diffusion of sized towns will bear the blunt of this future the government of India to achieve a turnaround centralized UWM urbanization growth(20),notably in the provi- in India's poorly served cities and towns(23). Whereas the need for reform in industrialized Sion of access to safe drinking water(Fig.2C) Apart from the lack of capital,there are also countries might still be a matter of debate,the and sewers(Fig.2A).High urban growth rates other,more general reasons why conventional proliferation of current UWM practices to the lead to high planning uncertainty,especially in UWM is not the best solution for rapidly growing Evapo Reuse transpiration -12% 1.7% II Stormwater Global drainage water Municipal supply water use Sewer j Urban 6tl 90°In ] 455 km�year' Sewer 10-40% discharge Industry a Loss from leaky pipes 739 km3,year' Sewage treatment plant 162% of urban Fig.1.The global urban water cycle.According to country-specific data from FAO(69),the global municipal water withdrawal is estimated to be 454.8 x 109 m3 year-'(184 liters person'day 1),and 738.8 x 109 m3 year 1(300 liters person-'day')for industrial use.This corresponds to 12%and 19%,respectively,of the total global water withdrawal.Shiklomanov(74)estimates global urban evapotranspiration to be around 12%.Typical water"losses"due to leaky supply systems are between 10 and 40%(69,75).Globally,around 1.7%[7.7 x 109 m3 year';from(36)]of the municipal water supply is reused in this way—mostly for irrigation. SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 929 SECTIONSPECIAL URBAN PLANET cities.Network-based infrastructures are designed [so-called transitions in socio-technical regimes they are nonexclusive,and there are many over- and built for "final design performance." High (32)].What is at stake,therefore,is a mainstream- laps and potential synergies between them. growth rates therefore impose large idle capacities ing of novel system alternatives in the UWM sec- during the early life of the infrastructure,with for that would respond to the challenges noted Stormwater drainage correspondingly high per-user costs(22).Further- above.A number of technological and institution- Urbanization means that not onlythe population more, high planning uncertainty also increases al approaches look promising.They represent po- but also the area in need of drainage increases.Es- the risk of sunk costs if the expectations of city tential foci of future innovation efforts.However, timates for 2000 to 2030 indicate an enlargement growth are not fulfilled or if not enough water is available for the correct functioning of the sewers. A Proportion of population connected to sewers The lack of stable energy supplies,spare parts, and know howfor reliable operation are additional factors that limit the expansion of centralized systems(24).As a special case,the improvement ; Of sanitation conditions in informal settlements in low-and middle4ncome countries has proved ;8 difficult because of disabling institutional envi- ronments,a lack of secure tenure and,rule of law, which often prevent private or public investments in infrastructure(25,26).In view of the expected increase in the populations of such informal set- tlements from today's 1 billion to 2 billion in 2030 (27),this is a quantitatively important situation with dramatic consequences not only for the ; inhabitants themselves,but also for the urban and natural environment. <20% 2130% -,31-45% 46-60% 61-80% 81-100% No data On the basis of those facts,we conclude that for ------------------------------------------------------------------------------------------------------------------ the areas with the highest rate of urbanization,there is an urgent need to develop more cost-effective and B Areas of physical and economic water scarcity resource-efficient systems that deliver the desired - water services of UWM without the prohibiting 4-;' ,: •�+ constraints of the conventional centralized system. Alternative solutions to conventional UWM As the currently dominant conventional approach '� a to UWM is unlikely to meet the challenges of an increasingly globalizing world[see also(28-30)], a shift toward a"new paradigm"is required(31). Three of the more salient candidates for new water paradigms that substantially depart from t, the present strategy are integrated water resources r management (IVVRM), adaptive management r (AM),and ecosystem-based approaches(EBAs) (31).A shared feature of these reform agendas Little or no Economic Approaching Physical No data is that they give primacy to organizational and water scarcity water scarcity water scarcity water scarcity institutional reforms in order to orient water ------------------------------------------------------------------------------------------------------------------ management toward providing sustainable water services rather than merely delivering quantities C proportion of population using improved drinking water sources of water.These approaches have gained traction in science and policy-making in recent years(31). �= - In particular,they have inspired new policy ap- proaches such as the European Framework Di w rective,or kindred approaches in countries like r ?' Australia,South Africa,and China.However,the impacts on real water systems have been limited (30,31).One reason is that the routines and prac- tices ofwater professionals are not directly deter- mined by planning discourses or governmental mission statements.Rather,they are oriented to technical expertise and the professional cultures s that have developed over decades in line with the 1 dominant UWM systems. This debate tells us that it is not enough to hope 0-80% 81-90% 91-95% " 96-98% >98% No data for technological breakthroughs or to believe in the wisdom of more inclusive governance arrange- Fig.2.Important global challenges of UWM.(A)Proportion of population connected to sewers(76). ments alone.Rather,the joint development of new (B)Areas of physical and economic water scarcity[data from International Water Management Institute institutional conditions and technological designs (IWMI);updated in 2015;map reproduced with permission from IWMI(77)].(C)Proportion of population is needed to ensure fundamental improvements using improved drinking-water sources(78). 930 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE ....................... i i of the global urban areas by an additional 60 to 200%(33).It is therefore no surprise that the lim- its of the conventional UWM approach were first recognized in stormwater drainage.Concepts such as sustainable urban drainage systems(SUDS),low- impact urban design and development(LIUDD), o water-sensitive urban design(WSUD),and green Dishwasher Kitchen tap Washing machine Shower Bathroom tap Toilet 000 infrastructures(GI)appeared in the scientific lit- erature toward the end of the 20th century(34). L[ The primary goal of these concepts is to maintain or reintroduce a more natural state of the urban Y 1 ® ® ® Y hydrological catchment,to reduce the impact Urine Feces Water of storrawater drainage on the aquatic environ- ment,and to reduce flood risk.All these concepts Heavy g y g greywater re water Light water Brownwater I introduce a strong element of decentralized mea- sures and emphasize the importance of long-term planning. Greywater Blackwater Increasing water productivity Fig.3.With source separation of wastewater in the household,new types of wastewater can be C This practice helps to reduce net water consump- constructed for optimal treatment.It is even possible to include treatment and recycling processes in tion and utilize the available water more efficient- a single device.This offers totally new perspectives for mass-produced,consumer-friendly wastewater ly.Three main strategies designed to increase treatment technology(for examples,see Table 2). water productivity are reducing water waste, down-cycling or reuse of lower-quality water, groundwater and for the targeted alimentation of Source separation of waste and regenerating high-quality water from used surface water(36).There are comparatively few Separating wastewater streams as early as pos- water(35). In the last two strategies,the col- large-scale direct potable reuse schemes,and these sible alleviates resource recovery and/or facilitates lected wastewater is in most cases treated in compete in terms of energy consumption and costs the treatment process.This can take place at the wastewater treatment plants to the desired qual- with desalination technology.The advantage of household level,but also at the level of a single ity,making it fit for reuse.Globally,around 1.7% this approach is its compatibilitywith conventional household device(Fig.3).In particular,the sep- [q.q x 109 m3 year-1;from(36)]of the municipal network-based UWM.However,it requires addi- aration of greywater promises new ways of re- water supply is reused in this way—mostly for tional infrastructure for treatment and redistri- using water. Compared with wastewater reuse, irrigation(Fig.1).In California,61%of the reused bution,thus increasing the energetic,financial,and greywater recovery involves smaller hygienic. 0.8 x 109 m3 year 1 of water is applied for irrigation, institutional burden.More innovative solutions are concerns,has a reduced"yuck"factor, and de- and the rest is mainly used for recharging the found in Table 2. mands less treatment effort.Especially in and Table 2.Examples of emerging solutions to UWM challenges. Increasing water productivity Distributed treatment Source separation of waste Reuse Substitution ............................................................................................................................................................................................................................................................................................................................................ Tap water supply PoI mer Housing area I' Y 0 OO beads A� El MW { Greywater Service =r Resource water s , I recovery,center Biowaste--► --i- Biosolids - Blackwater Service water Treatment Recyclables Recycling shower(70) Waterless washing machine(71) Distributed treatment of waste at district level(72) Blue Diversion Toilet(73) SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 931 SPECIALI URBAN PLANET A Centralized plants have been installed worldwide(45).Their performance has been judged as mediocre at best, Control, with some authors stating that their failures are regulation not primarily due to immature technology but rather to weak or unsuitable organizational models .10 and institutional setups(M).Whereas this may be partially true(see next section),many small-scale d technologies are little more than scaled Technology down con supply ventional treatment plants,originally developed 5 ' y with a very different set of requirements than we would imagine for small-scale technology. Professional installation, Institutional and organizational reforms . operation,service Multiple efforts on this front have been advocated ----------------- ------ ------------- ---------------------------------------------------------------- in the sector since the late 1980s(46).Great hopes Control, were originally placed in a stronger involvement B Decentralized Installation, regulation by private actors in service delivery and infra- operation structuremvestment.However,evidence about the Control, success of these reforms is mixed(47 50).Research regulation has shown that public and private organizations tot 0 Installation, can be equally effective and efficient in strategic operation planning(51),and that success of reforms depends ' g on how well competences of utilities and mstitu- € 0 tional context conditions are aligned with the tech- nologicalTechnology characteristics of the sector(52,53).For gY Installation, supply,service operation the case of distributed systems,this means that Control, innovation in organizational and regulatory models regulation is badly needed.The centralized management ap- proach,combined with centralized treatment tech nology,has been considered the most cost-efficient organizational and regulatory mode for most of the ------------------------------------------------------------------------------------------------------------------ 20th century(44)(Fig.4A).This is especially true C Contracting when it is compared to a fully decentralized ap- Technology proach,where end users are responsible for operat- Control supply ing their treatment plants and regulators have to regulation oversee innumerable individual installments(Fig.413). Recent advances in sensor and communication tech - nology,however,enable new contracting schemes Installation,operation,service �•�where central operators can monitor large fleets of individual appliances andthereby guarantee a very good performance in terms of effluent quality ---------------a o a ------ 6 and convenience for the end user(54). -._d_a_. Ways forward for policy and research Overall,any promising approach to solving the urban water challenges requires innovation and u 4 development processes in almost all technical,or- ganizational,and institutional dimensions.How- Fig.4.Alternatives for management of centralized and decentralized wastewater treatment plants. ever,the UWM sector seems to be very poorly (A)Fully centralized,(B)fully decentralized,and(C)contracting scheme for decentralized technology prepared to deal with innovations(55,56).The with centralized operation, legacy of the network logic,slow renewal cycles, and high long-term investments lead to risk aver- regions, greywater provides greater potential sons to apply this concept more broadly in order sion with respect to novel technologies.Little potable water savings than local stormwater cap- to render UWM more resource efficient(43). competence in innovation management has con- ture because it provides a steady source of water sequently been built up in most water utilities during periods with little or no rainfall(36,37). Distributed or on-site treatments (53).Policy-makers and end users have also been Not only water,but also energy and nutrients Decentralized systems have the advantage that they reluctant to accept disruptive changes,so that are more easily recovered from source-separated can be installed in the short term when needed,there- increased efforts are necessary to mainstream in- wastewater:energy from hot water(38)and from by reducing the requirement for large-scale invest- novations[compare direct potable reuse(57)]. feces(39)as well as nutrients from urine(40). mentin sewers and centializedwastewatertneatment Furthermore,a major international research and Some well-documented examples of source sep- plants.Moreover,they allow the local reuse of water policy effort is needed in the field of sustainable aration include the 40 million domestic biogas and therefore increase water productivity(Table 2). water futures(1).This represents a policy challenge reactors in China (41) or the almost 100,000 Also,the argument of lower costs of centralized on par with other processes of global change. urine-diverting dry toilets in peri-urban areas systems due to economies of scale at the treat- On-site treatment and source separation,espe- of eThekwini,South Africa(42).Although most ment plant has become much less persuasive in cially in combination,open up the potential for examples of source separation are still found in recent years(44).Over the last few decades,large locally adapted water services and the recovery areas without existing sewers,there are good rea- numbers of decentralized wastewater treatment and reuse of valuable resources.A good example 932 20 MAY 2016•VOL 352 ISSUE 6288 seiencernag.org SCIENCE ..._....... __ _ _ _.........................._...._.... is the"Reinvent the Toilet Challen ge"of the Bill recovery of wastewater to reduce dependence on 38.F.Meggers,H.Leibundgut,Energy Build.43,879-886(2011). &Melinda Gates Foundation,calling for the next Malaysian water resources(36),and in China,small- 39.G.Zeeman,K.Kulawa-Roeleveld,Water Sci,Technol.64, generation of on-site wastewater treatment tech- scale membrane bioreactors are proliferating to 1987-1992(2011). 40.T.A.Larsen,A.C.Alder,R.I.L.Eggen,M.Maurer,J.Lienert,nology.This call aimed to stimulate the academic provide enough water for its growing cities(68). Environ.Sci.Technol.43,6121-6125(2009). community to develop an innovative toilet for There will be no one-size-fits-all solution,but with 41.National Development and Reform Commission,"Medium and the urban poor with no requirement for conven- the immense challenges for UWM ahead of us,it long-term development plan for renewable energy in China tional network infrastructures(water pipes,sew- will be important to accelerate research efforts (translated from Chinese)"(Beijing,2007). 42.K.M.Udert et at.,Water S.A.41,212-221(2015). ers,electricity networks),while simultaneously and to profit from the lessons leaimed about Sue- 43.T.A.Larsen,J.Lienert,K.M.Udert,Eds.,Source Separation promoting maximal resource recovery and zero cessful innovations in other sectors. and Decmtraization for Wastewater Treabrient(IWA,London,2013). I€ emissions(58). 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ACKNOWLEDGMENTS has led to large-scale academic efforts to develop 36.B.Jimenez,T.Asano,Eds.,Water Reuse:An International We thank R.Siber from Eawag for help in preparing Fig.2.The the alternative resource Of stolmwater(66),whereas Survey of current practice,issues and needs,Scientific and authors declare that the publication of this paper presents no the aging infrastructure of the United States has Technical Report Series,no:20(IWA,London,2008). conflicts of interest.All present affiliations of all authors are led to Similar efforts in the area of infrastructure 37.National Academies of Sciences,Engineering,and Medicine, indicated. "Using Graywater and Stormwater to Enhance Local Water management(67).Singapore pursues Centralized Supplies:An Assessment of Risks,Costs,and Benefits"(2016). 10.1126/science.aad8641 SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 933 SECTIONSPECIAL URBAN PLANET PERSPECTIVE share of new diesel cars on London's roads,up from 1 in 10 cars in 2000 to 6 in 10 in 2014.Real- world NO2 emissions from most of these vehicles Transport solutions for cleaner air do not comply with European exhaust emission standards,which were introduced in 1993 to im- prove air quality(6). Frank J.Kelly'*and Tong Zhu2* A tale of two cities—Beijing In cities across the globe, road transport remains an important source of air In contrast to the I7Ks long industrial heritage, pollutants that are linked with acute and chronic health effects. Decreasing vehicle China has undergone rapid industrialization over emissions—while maintaining or increasing commuter journeys—remains a major the past few decades,adding thousands of kilo- challenge for city administrators. In London,congestion-charging and a citywide meters of urban road and hundreds of millions low-emission zone failed to bring nitrogen dioxide concentrations under control. of vehicles.PM2.5 emissions from traffic have con- n Beijing,controls on the purchase and use of cars have not decreased transport tributed to increasingly poor air quality in Beijing emissions to a sufficient extent.As cities continue to grow, not even (7),threatening public health(8).The severity of zero-emission vehicles are the solution. Moving increasingly large numbers air pollution in Beijing was first acknowledged of people efficiently around a city can only be achieved by expanding when China was bidding for the Olympic Games mass transit systems. in the 1990s.To address the problem,in 1998 the Beijing municipal government introduced the By facilitating the movement of people and To help achieve the first goal,a congestion- first of 16 stages of air pollution control measures. goods and providing employment,road charging scheme(CCS)was introduced in central Initial measures mainly focused on shutting down transport supports economic growth and London in February 2003(3).The CCS initially small industrial and domestic coal burning stoves plays a considerable role in global urban- reduced the number of private vehicles entering and controlling dust from road and construction ization.The consequent dependence on central London by 18%,but the scheme's effective- sites, as well as phasing out old vehicles that did fossil fuels(increasingly diesel in Europe)has, ness has since been eroded;since 2012,congestion not meet emission standards.These standards however,created specific air pollution challenges. has broadly been back at pre-2002 levels. were,however,much less strict than those in In particular,road transport remains an important The London-wide LEZ,introduced in February place today. source of particulate matter(PM)and nitrogen 2008,aimed to tackle the second goal by restric- Given fast urbanization and social and economic dioxide(NO2),which can cause or aggravate asth- ting the entry of the oldest and most polluting development in Beijing,later measures were more ma and impair lung development in children(1). vehicles(such as diesel engine heavy goods ve- comprehensive because they needed to deal with Here,we ask whether the policy interventions hicles,buses and coaches,and larger vans and the complicated nature of the air pollution sources already introduced,or under consideration,in minibuses)across greater London(4).However, in Beijing.Long-term and strategic measures in- two of the world's largest and most economically although black carbon pollution has gradually cluded replacing coal with natural gas,creating a powerful cities—London,England,and Beijing, decreased on many roads in London since 2008, public transport system with 554 km of subway, China—are good exemplars for other cities to NO2 concentrations have either not changed or and introducing current European emission stan follow(Figs.1 and 2).We consider some of the have gone up(5).As a consequence,London does dards.During the Beijing Olympics in 2008(9) changes required so that urban areas do not grind not comply with European Union limit values for and the Asia-Pacific Economic Cooperation meeting to a standstill because of continued growth and NO2 and is unlikely to do so until 2025 at the in Beijing in 2014y aggressive measures were taken transport demand. earliest.The main reason for this is the increased to reduce the number of vehicles on the road by A tale of two cities—London In view of widespread public concern about the health effects of air pollution,the mayor of London launched an air quality strategy in t 2002, entitled Cleaning London's Air(2).The main aim of the strategy was the reduction of pollution from road traffic,which was the largest j? source of the pollutants of concern—PM2.5 and NO2—in the city.PM2.5 refers to particles that pass through a size-selective inlet with a 50%ef- ficiency cutoff at 2.5 µm aerodynamic diameter, which means that they are small enough to pen- _ ,ll etrate deep into the lungs.To this end,the goals - were to reduce the number of vehicles on the road and to lower emissions from individual vehicles — -- through modernization of the fleet vehicle stock 'National Institute for Health Research(NIHR),Heath Protection Research Unit in Health Impact of Environmental ii �i i1S3ti Hazards,MRC-PHE Centre for Environment and Health, z King's College London,London SE19NH,UK.2State Key a Laboratory for Environmental Simulation and Pollution Control,College of Environmental Sciences and Engineering, w and Beijing Innovation Center for Engineering Science and Advanced Technology(BIC-ESAT),Peking University,Beijing Corre Fig.1.Tower Bridge,*Corresponding author.Email:frank.kelly@kcl.ac.uk(F.J.K.);,China.* Brid the Shard,and City Hall.London continues to experience road congestion as o Corre a zhu@pku.edu.cn(T.Z.) it struggles to deal with an ever-increasing population. 934 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE . . .-.....__-...---.... r allowing cars to be used on only certain days of �l the week, determined by the last digit of the car license number. This measure resulted in substantial temporary reductions in congestion _ and pollution concentrations in Beijing and was s considered so successful that it was made a routine A - rule immediately after the Olympics.Today,every car is allowed to drive 4 days per 5 weekdays. These efforts to control air pollution in Beijing I have shown some success.PM2.5 concentrations - - have started to fall in recent years. However, m these benefits have been compromised to some ® �� extent by the rapid growth in vehicle numbers from 1.5 million in 2000 to 5.6 million in 2015. �� To start dealing with this problem,the Beijing s government introduced a range of vehicle emis- _ Q Sion policies,includ ing ding a lottery system for new car license plates and further modernization of the fleet. - Given that the vehicle fleet in China,especially in Beijing,now has the most advanced engine j technologies(10),further control measures to cut vehicle emissions will necessitate further restric- tions on car movements.Importantly,the Chinese government has not provided incentives for in- Fig. 2. Galaxy Soho. Beijing's increasing private car ownership is contributing to air pollution creasing the proportion of private diesel vehicles challenges. (11).As a result—in line with other countries, such as Japan—the problems of diesel NO2 emis- sons from private vehicles contributing to Beijing's flows near these toll plazas were linked to more electric vehicles.Worries over battery life and the poor air quality have been avoided. healthy infants born to mothers living nearby(15). lack of coordinated charging networks have,how- Other interventions,such as the Hoy No Circula ever,held back vehicle sales,even with generous Looking to the future (HNC) program in Mexico City, have proved government subsidies.In the UK,the electric ve- The experiences in London and Beijing clearly hicle fleet has gtown in the past 2 years from 3500 show that more fundamental changes in urban to more than 50,000 vehicles,suggesting that the transportation systems are required for air quality tide is turning irir rovements to be achieved and for city streets in favor of zero-emission vehi- P tY a cles.In contrast,goals for fuel cell(hydrogen)- to become more pleasant environments.In London, AS CItZeS COtitlnile t0 u7 In p � powered cars have not been achieved because the introduction of an ultralow emission zone Size and population, even of limited fueling networks and high initial ve- (uLEZ)is planned for 2020(12).However,ban- hicle costs. ning all but the cleanest vehicles and incentivizing Zero emission vehicles are As cities continue to grow in size and pop- the use of zero-emission cars and taxis in a small not the Solution. Moving ulation,even zero-emission vehicles are not the area of central London will be insufficient to increasing numbers Of solution.Moving increasing numbers of people achieve compliance with NO2 standards until at af�Clem efficiently around a city can only be achieved by least 2025(13).Beijing will grind to a standstill people efficiently ly around expanded mass transit systems. The increased through excessive congestion,and air quality will a city can only be achieved use of bus networks and traditional subways are suffer further if car ownership levels are allowed b anded mass t7Yi11Slt providing city dwellers with more flexible,cheaper, to move toward U.S.levels(840 cars per 1000 Y �� and less polluting options. For instance, China people).Car ownership(currently 280 per 1000 systems. is building 87 new mass transit rail lines over people)must therefore continue to be strictly the next 5 years.If construction continues at this controlled. pace,China's cities will have half of the world's In many.European cities,attitudes toward car less successful.Introduced in 1989 to address metro tracks by 2050(17). ownership appear to be changing.Many urban the severe air pollution problems in Mexico City, Rapid transit systems offer only a partial so- youth of today,it seems,would rather use taxis the HNC banned most drivers from using their lution to city congestion and poor air quality, and car share than own their own car.Recent vehicle I weekday per week,determined by the however,because many users may not live within polls in London associated with the mayoral elec- last license plate digit(16).Although the program easy walking distance to the transit points.To be lions in May 2016 put air quality issues high on was largely successful in removing-20%of ve- effective,rapid transit systems must be linked with the political agenda and suggest that there is pop- hicles from the roads,no evidence could be found other transport options at the start and end of the S ular support for a further tightening of vehicle use that it led to increased use of public transporta- journey.The creation of Autonomous Mobility- W in the city.Cars promote a sedentary lifestyle,and tion or that it improved air quality(16). on-Demand networks may solve this problem(17). a shift to cycling and walking has health benefits The car industry has recognized the need for Modeled after bicycle-share progiams,users would & for urban dwellers(14). change,and companies such as BMW and Ford have access to a network of lightweight electronic o Upon recognizing the negative impacts that have launched car-share schemes.Car-sharing has vehicles(LEVs)distributed at charging stations z congestion,when entering cities,has on the econ obvious benefits to cities.Zipcar estimates that throughout the city.Customers could summon omy and on air quality, several states in the every shared vehicle replaces up to 20 private cars, a vehicle through a smartphone app and abandon = northeastern United States have introduced elec- thus reducing total vehicle miles and land devoted it upon reaching their destination,from where o tronic toll collection technology,which has helped to parking.The car industry is also pushing for- the vehicle would find its way back to a charging o to reduce delays at toll plazas.Improved traffic ward the development of city-friendly plug-in station or new user.Trials of this technology are i SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 935 SPECIAL SECTION URBANPLANET planned in California and in Milton Keynes,UK PERSPECTIVE (18,19). In the city of the future,mass public transport systems may lead to many more car-free roads, The ecological future of cities transforming the landscape and enhancing the urban experience.Moving toward such an envi- Marls J.McDonneW*and Ian MacGregor-ForS2* ronment depends,however,on continued and exacting scientific research,the translation of The discipline of urban ecology arose in the 1990s,primarily motivated by a widespread interest such research into realistic and effective poli- in documenting the distribution and abundance of animals and plants in cities.Today,urban cies,and successfully encouraging members of ecologists have greatly expanded their scope of study to include ecological and socioeconomic the public to use public transport, value ex- processes,urban management,planning,and design,with the goal of addressing issues of ercise, and not drive for short journeys (20). sustainability,environmental quality,and human well-being within cities and towns.As the The reward will be improved health and quality global pace of urbanization continues to intensify,urban ecology provides the ecological and of life for the growing urban populations around social data,as well as the principles,concepts and tools,to create livable cities. the world. or the past half century,the prevailing global acting physical,biological,and social components REFERENCES economies have created employment oppor- at city-or ecosystem-wide scales(5).For example, 1. 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ExtremeTech,"Google's new self-driving car:Electric,no portunities to test fundamental Social and eco- steering wheel,and incredibly cute'(2014);available at www. 'Australian Research Centre for Urban-Ecology,Royal extremetech.com/extreme/l93174-googles-new-self-driving- Botanic Gardens Victoria and School of BioSciences, logical questions,such as the effect of landscape car-electric-no-steering-wheel-and-incredibly-cute. University of Melbourne,Melbourne,Victoria 3010,Australia. fragmentation on the distribution of organisms, 20.F.J.Kelly,J.C.Fussell,Environ.Geochem,Health 37,631-649 2Red de Ambiente y Sustentabilidad,Institute de Ecologfa,A.C. the effect of night lighting on the cireadian rhythms (2015). (INECOL),Carretera Antigua a Coatepec 351,El Haya,Xalapa of humans and other organisms,and the role of 91070,Veracruz,Mexico. *Corresponding author.Email:markmc@unimelb.edu.au(MJ.M.); urban green spaces in providing ecosystem services 10.1126/science.aaf3420 ian.macgregor@inecol.mx(I.M:F.) to urban dwellers.Cites also provide opportunities 936 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE Y I u „ a a , 4 e w ` Y e' ,S. , l l3 t• 'III � _- _ �' �A �Mc ry� i F <u, V E iV a w . i i s' n e' t : 3 Fig.1.View of the central business district and Kings Domain gardens in Melbourne,Australia. Like other cities around the world, Melbourne is developing urban ecology action plans to improve quality of life for both humans and other species in the region. for learning about people's knowledge,attitudes, Global ecological assessments on the distribu- (United States),Singapore,Durban(South Africa), and values in regard to nature.Increasingly,ecol- tion of plants and animals in urban environments and Portland(United States)—are incorporating ogists and landscape architects work together to have documented the biological richness of cities similar strategies and plans. develop urban design experiments that deliver and offered insights into maintaining this rich- Local governments have been participating in both cultural amenities and important ecological ness.For example,Aronson et al.(12)found that research partnerships focused on diverse themes information(7).For example,in design experi- the presence of remnant and restored natural veg- such as understanding,protecting,and enhancing ments initiated to increase urban tree cover,ecol- etation is important for maintaining bird and plant biodiversity, creating and managing ecological ogists are active participants in the design process populations in urban areas.Hahs et al. (13)re- linkages;creating biodiversity-friendly environments as well as the follow-up assessments. ported that fewer local plant extinctions occurred by minimizing negative effects on animals,plants, Due to the many physical,biological,and social in cities that maintained at least 30%native veg- soils,and ecosystems;and assisting the public in variations between different cities,urban areas etation cover.Unfortunately,few studies have ad- experiencing and valuing biodiversity and urban w also provide unprecedented opportunities to study dressed the ecological effects of urban growth in ecology in general.The Chicago Wilderness re- the evolutionary and adaptive processes affecting developing countries,where levels of biodiversity gional alliance is one such partnership.This group N urban biota For example,in a recent global com- are highest and urbanization is progressing rap- aims to improve the quality of life of both humans parative study of more than 800 species of urban idly(14). and other species in the region.Initially,research- birds,Sol et al.found that species loss was pri- ers,government and nongovernment agencies, IQ as marily due to the birds'inability to adapt to urban Urban ecology in action and the public came together to restore and en- conditions,especially with regard to exploiting Urban ecology research commonly has an applied hance the region's biodiversity.Their mission o novel resources and avoiding new risks(8).How- outlook,with a focus on identifying mitigation has expanded to include issues related to climate ever,other studies have shown that some species and adaptation strategies to reduce the negative change,green infrastructure,and connecting peo- currently thriving in cities have adapted to urban effects of human activities(3).Urban ecologists ple with nature. environments via behavioral,physiological,mor- in Melbourne,Australia,have begun to develop ac- Increasingly,urban ecologists,local communities, m phological,and evolutionary responses(9).Ex- tion plans to improve the health,livability,resilience, and governments are also working together in w amples include great tits(Paws mcdorn)modifying and sustainability of their city(Fig,1).For example, developing countries.For instance,Chilean re- ztheir song to communicate at noisy locations(10) an urban forest strategy aims to ensure that the city searchers conducted detailed studies of urban a and plants living in highly fragmented urban en- will have a resilient,healthy,and diverse urban wetlands in Valdivia(southern Chile).Their ac- o vironments shifting to localized seed dispersal forest in the future.Other cities around the world— quired environmental and social knowledge en- strategies(11). including London(United Kingdom),Chicago couraged the local government,together with the SCIENCE sciencemag.org 20 MAY 2016,•VOL 352 ISSUE 6288 937 SPECIAL SECTION URBAN PLANET interested community,to develop a land manage- PERSPECTIVE ment and planning tool for the protection and future sustainable use of the region's wetlands.Another example is that of one of the remaining Li i • • Living n cities, naturally perennial springs(I-a;Carbonera)surrounding the city of Queretaro,located in a semi-arid region of Teriy Hartipl and Peter H.Kalm Jr.2 central Mexico.Because the area's wetlands have been studied for several years,it was possible to Natural features,settings,and processes in urban areas can help to reduce stress rescue the spring,together with strong local stake- associated with urban life.In this and other ways,public health benefits from,street trees, holder support and action.This is clearly a suc- green roofs,community gardens,parks and open spaces,and extensive connective cessful case in which locals worked closely with pathways for walking and biking.Such urban design provisions can also yield ecological academics to achieve a common goal.This peri- benefits,not only directly but also through the role they play in shaping attitudes toward the urban spring has been managed,and the area is environment and environmental protection.Knowledge of the psychological benefits of currently used to conduct recreational and educa- nature experience supports efforts to better integrate nature into the architecture, tional activities while also contributing to the re- infrastructure,and public spaces of urban areas. storation of several critical ecological processes. Toward livable cities rowding,noise,and other The discipline of urban ecology has made great stressful urban condi- strides over the past three decades.To further tions increase the risk of our knowledge of urbanization's effects on people, mental disorders such as biodiversity,and ecosystem processes,urban ecol- anxiety and depression ogists must shift from studying patterns to un- (1).However,urban areas also tangling the emerging mechanistic processes have environmental assets that behind the reported patterns(15).However,it support mental health.For ex- is also crucial to create the tools and procedures ample,parks,green spaces,street for transforming scientific knowledge into action. trees,and community gardens The need for these advances is pressing,as there can facilitate physical activity, is a growing discontent among urban dwellers social contacts, and stress re- worldwide,related to the erosion of their quality duction(1,2).How can psychol- of life.Many urban dwellers are now calling for ogical benefits from encounters =x the creation of green,sustainable cities that are with natural features and pro- also healthy and resilient(16).Incorporating urban cesses offset the psychological ecology principles into the design,construction, costs of other urban living con- and management of cities will require the co- ditions?Answers to this ques- operation, alliance, and synergy of all stake- tion will help improve the quality holders, thus reforming the way we conceive of life of today's growing ur- and prepare land to fulfill the needs of modern ban populations(2,3)(Fig.1). human agglomerations. 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United Nations Human Settlements Programme(UN-Habitat), 'Institute for Housing and Urban Research and Department conditions in rural areas Support health.Peen m State of the World's Cities 200812009.Harmonious Cities of Psychology,Uppsala University,Uppsala,Sweden. et al.(5�performed a meta analysis of 21 Studies, o (Ea thscan,2008). andForestDepartment of Psychology and School in Environmental done after 1985,that investigated the prevalence o and Forest Sciences,University of Washington, 10.1126/science.aaf3630 Seattle WA,USA. of mood disorders among non-institutionalized a 938 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE adults in relatively affluent countries.They found Findings of urban-rural differences in mental icized for neglecting relevant forms of variation that the odds of mood disorder were 28%higher disorders might be taken as warnings about the (8).Experimental evidence regarding plausible in the urban areas than in the rural areas;how- consequences of urbanization,but there is a risk mechanisms has nonetheless encouraged large ever,the results were highly heterogeneous, per- of confusing cause and effect.The social,political, observational studies on urban green space and v haps because "rural' and"urban"were defined and economic forces that drive urbanization in a health.Such studies consider plausible cumu- differently in different studies.They recognized the particular society may also generate mental illness lative effects of green space and greenery near problem with integrating results when urban through other mechanisms.,For example,in some an urban home.Most such studies focus on quan- settings in some studies resemble rural settings countries, many people have left rural areas for tity,but some have also used quality indicators in others. urban ones under threat of violence;this appears (9).Most of the observational studies have used a Judd et al.(6)have argued that binary urban to have boosted the prevalence of major depressive cross-sectional design,but recent longitudinal and rural categories are insufficient.Numerous disorder(7).Poor conditions in the spontaneous studies have enabled stronger inferences regard- environmental factors can affect the stress that settlements they create may exacerbate the effects ing beneficial effects of access or proximity to na- people experience in urban and rural settings of victimization,disruption of social relations,and ture.For example,using 5 consecutive years of and, thus, the prevalence of disorders such as loss of traditional occupations,but urbanization data for each of 1064 participants in the British anxiety and depression.These include,for exam- itself is not the initial cause of disorder. Household Panel Survey,Alcock et al.(10)showed ple,residential density,housing quality,air qual- that those who relocated from a less green(58% ity,transportation options,access to health and Psychological benefits of nature experience local area coverage)to a more green(74%)urban welfare services,and access to parks and green Research on the experience of nature also sug- area showed improved mental health over the r spaces.All of these factors might play a role in gests that urban living conditions can under- next 3 years.In contrast,those who moved from mine mental health,whereas more(74%)to less(59%)green urban areas showed relatively natural conditions a decline in mental health before the move,fol- can support it.The term"na- lowed by a return to the pre-move baseline. r " a ture" means different things Much research on nature experience assumes lu �, in different contexts. Recog- that too few generations have passed for natural nizing personal and cultural selection to shift the adaptedness of affective and i; aspects of the experience of cognitive functioning from the conditions of hom- '- „ nature,psychological research inid evolution(8),and that humans are therefore x considers how different peo- poorly adapted to living in urban environments, ple encounter nature in diverse broadly defined.This natural-urban antithesis l contexts,from viewing indoor neglects the fact that urban environments include plants in urban offices to walk- settings that are supportive of human function- ing in wilderness areas. ing;noisy,polluted,car-filled streets lined by anon- A significant portion of this ymous towers are not representative of all urban � research concerns the restor- - possibilities.This false antithesis also neglects rea- ative effects of nature experience, sons why people gathered in cities millennia ' such as regaining the ability ago,and the consequences of that move for the to concentrate and reducing interplay of natural selection and sociocultural - blood pressure after intensive development.Here too,the environmental catego- ` mental work(3, 8).Theories ries and the urbanization process need closer about restoration describe how examination. '= encounters with nature involve psychological distance from The design of cities and ,�.` " ��i�«" _ � ; • "`��'* "� everyday demands and inter- human-nature relations ested engagement with environ- Psychological research has substantiated long- mental features and processes. standing p reasoning about parks and green spaces These components of restor- as health resources for urban populations(8,11,12). ative experience have counter- This reasoning has xp g guided the creation of parks parts in many analyses of why in many cities,such as Central Park in New York people engage in outdoor rec- and Mount Royal Park in Montreal. Extending � reation, done in the United such precedents,researchers,design professio- " 9 States and elsewhere since the nals, citizen groups, and others are working early 1960s(8). Complement- together to create sustainable urban fabrics in ing what people have long said our increasingly urbanized world These efforts— they seek through outdoor rec- under banners such as green urbanism,green Fig.2. People living in cities can encounter nature in the context of reation and substantiating infrastructure,biophilic design,and renaturing— many different activities.Their experiences can enhance their devel- theoretical claims,laboratory seek abetter synthesis of natural processes and N opment,health,and well-being,and they can shape their attitudes and field experiments have re- ecosystem functions with architecture and urban toward the environment and environmental protection. peatedly shown that spending infrastructure through acts of creation,preserva- time in natural environments tion,and ecological restoration.Such efforts are whether a given individual develops a disorder, or viewing scenes of nature can quickly help people needed for psychological as well as ecological but they may do so in different ways in different to.lift their mood,improve their ability to direct purposes. The evidence mentioned above and > combinations.Together with individual vulner- attention, and reduce physiological arousal to a more like it warn against assuming that people z abilities and broader contextual characteristics, greater degree than do urban streets and other can simply adapt to increasing urban density and 2 research must consider the independent and com- comparison conditions(2,8). its concomitants without negative consequences 19 bined effects of these factors in order to elucidate As in studies of urban-rural differences in men- for health and well-being. opportunities how specific urban conditions may undermine or tal disorders,comparisons of single examples of By providing opportities for people to ex- 0 support mental health. urban and natural environments have been crit- perience nature in cities and to experience cities SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 939 I SPE CIA L SECTION URBAN PLANET as natural,such efforts can shape attitudes toward PERSPECTIVE the environment(Fig.2).People in increasingly large and dense urban areas may have few or no contacts with the natural world in everyday life. Meta-principles for developing smart, Environmental generational amnesia refers to the psychological process whereby each genera- sustainable and healthy cities es tion constructs a conception of what is environ- mentally normal based on the natural world encountered in childhood(13).A problem arises Anu Ramaswami,'*Armistead G.Russell,2 Patricia J.Culligan,- insofar as,the amount of environmental degra- Karnamadakala Rahul Sharma,'Emani Kumar4 dation increases across generations, but each generation tends to take that degraded condition Policy directives in several nations are focusing on the development of smart cities,linking as the nondegraded condition: the normal ex- innovations in the data sciences with the goal of advancing human well-being and perience.This helps to explain inaction on en- sustainability on a highly urbanized planet.To achieve this goal,smart initiatives must vironmental problems;people do not feel the move beyond city-level data to a higher-order understanding of cities as transboundary, urgency or magnitude of problems because the multisectoral,multiscalar,social-ecological-infrastructural systems with diverse actors, experiential baseline has shifted.Providing op- priorities,and solutions.We identify five key dimensions of cities and present eight portunities for people to experience more robust; principles to focus attention on the systems-level decisions that society faces to transition healthy,and even wilder forms of nature in cities toward a smart,sustainable,and healthy urban future. offers an important solution to this collective loss of memory and can counter the shifting baseline y the year 2050, the number of people With infrastructure as the focus, we identify (14). Such opportunities include, for example, living in cities is expected to increase by five key dimensions of cities and present eight large green spaces and parks,rivers restored to about 2.5 billion (1). It is estimated that principles to help guide urban transforma- some former free-flowing condition,expansive over 60%of the urban areas that will exist tions toward sustainability and health, draw- views over water and land,and extensive con- by 2050 have yet to be built,indicating ing on examples from the United States,China, nective pathways for walking and biking. that there will be massive new infrastructure and India. Thus,cities designed well,with nature in mind requirements, particularly in Asia and Africa and at hand,can be understood as natural,sup- (2). Simultaneously, existing cities worldwide Key dimensions portive of both ecosystem integrity and public are aging and much in need of infrastructure Economic opportunity is a key driver for urban- health.Further psychological studies can describe replacement. ization,and infrastructure is a prime enabler. how specific improvements in available oppor- Infrastructures-defined broadly as the systems Multi-city data sets are emerging that describe tunities for nature experience come to affect that provide water, energy,food,shelter,trans- scaling relationships among urban population mental health and environmental attitudes(15). portation and communication,waste management; growth, gross domestic product (GDP),house- How will they change if car-clogged spaces give and public spaces(3)-are essential to support hold incomes,and infrastructure-related param- way to natural places where children can play human well-being and economic development. eters such as financial investments,energy and wildly and others reflect quietly? However,aggregated globally,these seven infra water use,and land and road expansions(5). structure sectors currently place alarge burden Cities with different economic structures(e.g., REFERENCES on the environment and have a considerable im- highly industrial,highly commercial,or mixed 1. American Psychological Association Task Force on Urban pact on human health(Fig.1).Urban demands economy)are known to exhibit different soeio- Psychology,Toward an Urban Psychology:Research,Action,and dominate these effects; for example, -70% of spatial patterns of development(i.e.,urban form) Policy(American Psychological Association,Washington,DC,2005). global greenhouse gas(GHG)emissions are at- that affect infrastructure design.Yet basic city-level 2. T.Hartig,R.Mitchell,S.de Vries,H.Frumkin,Annu.Rev.Public Health 35,207-228(2014). tributable to cities(1).Because physical infra- data on urban GDP,sectoral employment,and 3. European Commission Directorate-General for Research and structures have life spans of 30 to 50 years,the household incomes are sparse in many developing Innovation,Towards an EU Research and Innovation Policy large imminent global requirement for new urban nations and in smaller cities and towns,where Agenda for Nature-Based Solutions and Re-Naturing Cities:Final infrastructure presents a historic opportunity for much urban growth is projected to occur. Report of the Horizon 2020 Expert Group on'Nature-Based Solutions and Re-Naturing Cities'(European Commission, change. The question is,how can urban infra- Urban form or morphology describes the evoly Brussels,2015). structure transformations in the 21st century ad- ing interaction between physical space and hu- 4. S.Milgram,Science 167,1461-1468(1970). Vance the environmental sustainability and human man activity in cities.Numerous data sets,from 5. J.Peen,R.A.Schoevers,A.T.Beekman,J.Dekker,Acta well-being of our cities by taking advantage of census data to aerial and satellite photographs Psychiatr.Scand.121,84-93(2010). 6. F.K.Judd et A,Aust.N.Z.J.Psychiatry 36,104-113 the enormous potential offered by data science and remote sensing information, are being in- (2002). and technology? tegrated to enable planners to characterize urban 7. A.J.Ferrari et al.,Psychol.Med.43,471-481(2013). Although information and communication form. Urban complexity science is advancing 8. T.Hartig et al.,in Forests,Trees and Human Health,K.Nilsson technologies are important for developing smart, new measures(4)that focus not only on pop- et al.,Eds.(Springer,Dordrecht,2011),pp.127-168. 9. S.M.E.van Dillen,S.de Vries,P.P.Groenewegen, sustainable,healthy cities(4),we argue that a ulation density,connectivity,proximity to jobs P.Spreeuwenberg,J.Epidemiol.Community Health 66,e8 larger understanding of urban infrastructure and services,and diversity and intensity of urban (2012). systems is necessary to move from data to infor- activities but also on understanding self-similarity 10. I.Alcock,M:P.white,B.W.Wheeler,L.E.Fleming, mation to knowledge and,ultimately,to action across scales(from blocks to neighborhoods to M.H.Depledge,Environ.Sci.Technol,48,1247-1255(2014). 11. T.S.Eisenman,J.Plann.Hist.12,287-311(2013). for urban sustainability and human well-being, cities) and patterns of social segregation(e.g., 12. D.C.Rouse,I.F.Bunster-Ossa,Green Infrastructure:A of migrant and informal populations in a city). Landscape Approach(Planning Advisory Service Report 571, Urban form represents the foundation upon American Planning Association,Chicago,2013). 'Hubert H.Humphrey School of Public Affairs,University of which infrastructure develops,shaping energy 13. P.H.Kahn Jr.,Technological Nature:Adaptation and the Future Minnesota,Minneapolis,MN 55455,USA.2School of Civil and of Human Life(MIT Press,Cambridge,MA,2011). Environmental Engineering,Georgia Institute of Technology, and material use; access to and contiguity of 14. P.H.Kahn Jr.,P.H.Hasbach,Eds.,The Rediscovery of the Wild Atlanta,GA 30332-0355,USA.-Department of Civil water bodies, green space, and other critical (MIT Press,Cambridge,MA,2013). Engineering and Engineering Mechanics,Columbia University, ecosystems;and urban equity and well-being. 15. F.G.Kaiser,T.Hartig,A.Brugger,C.Duvier,Environ.Behay.45, New York,NY 10027,USA.41CLEI-Local Governments for Infrastructure design and socio-spatial dis- 369-398(2013). Sustainability,South Asia Secretariat,New Delhi 110020, India, panties within cities are emerging as critical 10.1126/science.aaf3759 *Corresponding author.Email:anu@umn.edu determinants of human health and well-being. 940 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE ......_..... _ _ _...._._..__-.. I Cities are grappling with multiple and multi- supply chains and what the risks are to cities key dimensions outlined here—economic oppor- scalar health risks pertaining to infrastructure, from supply disruptions. Cities are beginning tunity,urban form,social-infrastructural dis- such as food and water insecurity in house- to track their transboundary greenhouse gas parities and human well-being,transboundary holds,neighborhood designs that inhibit active infrastructure-environment dynamics,and cross- living, regional air and water pollution, and scale multisector governance—serve as the frame- extreme heat, cold, and flooding that may be work(Fig.2)from which we draw principles for exacerbated by climate change(6).Socioeco- action. nomic disparities often shape exposure to the �1.1a larger understanding E various risk factors and mediate and modulate of urban infrastructure Basic principles for transforming cities the health outcomes.Addressing these diverse 1)Focus on providing and innovating basic infra- social,environmental,and infrastructural risk systems is necessary to move structure for all.Basic and affordable water,energy, factors represents a new paradigm for urban from data to information to sanitation,and transportation have long been rec- public health.The World Health Organization ognized as important for all cities but have been (7) and the Centers for Disease Control and knowledge and, ultimately, difficult to attain in some cases,often because of Prevention in the United States(8)recommend to action for urban rapid in-migration,unplanned urban expansions, community-based participatory health planning sustainability and human and challenges in infrastructure financing. With that connects local capacities with infrastruc 30 to 40%of the population in several cities in ture, using advanced information processing well-being." Asia and Africa living in slums(2),a healthy city G systems and ambient sensing. Making these must prioritize basic infrastructure for all.Many connections is challenging,requiring overarch- smart-city discussions focus on high technology, 3 ing frameworks that connect diverse data and footprints(11)while incorporating supply dis- overlooking more basic,yet innovative,equitable processes across scales to support action(9). ruptions(e.g.,power cuts,water scarcity,and food solutions that are emerging, such as fit-for- The environmental impacts of cities are nu- and fuel disruptions) into urban quality-of-life purpose point-of-use household water treatment merous and multiscalar, driven by the trans- metrics(12). in Chinese cities(14),water"ATMs"in Indian boundary nature of their infrastructure.Cities The intertwined outcomes of environmental cities, and prioritization to support nonmotor- produce less than 10%of their food and rely on sustainability and human well-being require under- ized transportation in compact mixed-use urban water,energy,fuel,and construction materials standing interactions among all seven sectors neighborhoods. from external sources. Sustainable urban sys- within a city in terms of local-scale quality-of-life 2) Pursue dynamic multisector and multi- tem studies are advancing urban supply-chain impacts;at the same time,it is also necessary to scalar urban health improvements,with atten- footprinting techniques that capture infrastruc- connect the transboundary infrastructures with tion to inequities.Cities must strive to address ture use within the city(shaped by economic regional and global environmental and health health priorities,which vary widely across cities, activity and urban form)in combination with impacts,engaging multiple actors and institutions within cities, and over time, by considering transboundary infrastructure supply chains and across scales (Fig. 2). Understanding and en- infrastiuctural,environmental,and sociocultural trade networks. Such transboundary footprints hancing the capacity of social,policy,and go- determinants at different scales(9).Such an (10)characterize the broader environmental im- vernance networks therefore holds the key to approach could yield,for example,regional weath- pact of all seven urban infrastructure sectors on change.Analyses of social norming and social net- er and air pollution forecasts that provide cus- various resources(e.g.,energy,water,and nutri- works are yielding insights about peer learning tomized messaging to vulnerable populations, ents)and on pollution.Transboundary analysis with respect to environment and health in cities; neighborhood-level health interventions, more considers how cities can reduce environmental mapping of policy actors reveals how information equitable access to nutritious food and green impacts within their boundaries and across their is shared across sectors and scales(13).The five spaces, and greater attention to sociocultural 86.6% 96.7% 19.5 million* 100 Disasters and extreme events 20 c 90 C 80 Buildings/shelter materials = &public spaces Childhood underweight,diets 16 c c 70 low in fruits&vegetables Food supply(agriculture,livestock) c 60 12 a1°i 50 aA Transportation(vehicle operations) Accidents&reduced mobility 40 µ a 30 Municipal water supply/ 8 CL waste&sanitation c 20 Air pollution/indoor&outdoor 4 10 Energy supply(residential, commercial,&industrial) z 0 _ 0 Global anthropogenic Global water Global infrastructure-related mortality GHG emissions withdrawal (2010) (2010) (2010) Fig.1.Impacts of key infrastructure sectors.Shown are the impacts of urban infrastructure sectors on global anthropogenic GHG emissions (20), global water withdrawals(21,22),and global disease burden(6).GHG and water impacts associated with buildings and shelter materials include those of producing cement and steel,disaggregated by the authors based on various literature sources. Non-energy GHG emissions are shown for waste and sanitation.Transportation-related premature mortality is from accidents(23)and reduced mobility(6).The asterisk indicates that total deaths in the right column are non-additive because of overlap. SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 941 SPECIAL SECTION URBAN PLANET r � Boundary of City 1 Larger food,water,energy& � Global trade& transportation networks ` environmentally extended Local infrastructure provision ` input-output analysis leBuildings , Cit 4 � City 2 y Green/public j spaces Energy supply City 3 m City n LE � / f Waste and I ' sanitation 01 Transportation / J ""sib 0 91a►`y Municipal Food supply water supply j Ecological l / limits Home Neighborhood City Actors&ilnstitutions >Region/Nation - Globe Outcomes Local livelihoods,health and well-being -Transboundary impacts on environment,well-being and climate change Fig.2. Intersection of human activities and seven infrastructure sectors within a city, linked to natural ecosystems through transboundary infrastructures across scales.Actors and outcomes(health and sustainability)are also intertwined across scales. assets that enhance quality of life and human short periods of time,greatly reducing resource with which they must operate is key.For example, well-being. intensity(16). neighborhood-scale urban farms,solar gardens, 3)Focus on urban form and multisector syn- 5)Integrate high-and vernacular technologies. and waste management systems will require new ergies for resource efficiency. As populations Cities should seek local knowledge and systems- levels of coordination among homes,neighborhood urbanize,they become wealthier,increasing Ina- level understanding of different solution config- associations,businesses, and city-and state-level terial consumption and environmental impact, urations. For example, municipal plants that governments.At the same time,technology can To counter these effects,urban areas must in- convert solid waste to energy are not as effective change institutions; for example, widespread crease resource efficiency,not by a few percent- in developing world cities.The waste streams deployment of sensors is enabling remote sur- age points but by factors of 4 to 10. Such have lower calorific value,having been sifted veillance of distributed water and wastewater efficiency gains cannot come from single-sector through by the informal sector of waste pickers systems. Awareness of the need for new and interventions in a diffuse urban morphology.Re- who recycle more than 200 types of waste paper evolving institutions to manage emerging smart search suggests that an optimally dense urban and plastics,which creates greater systems ef- infrastructure can help ease these transitions. form,with a high intensity of diverse co-located ficiency in terms of material cycling while also 8)Create capacity and transparent infrastructure activities,creates opportunities for systemic multi- promoting local livelihoods. Formalizing and governance across sectors and scales.Cities need sector infrastructure interventions,yielding the integrating the expertise of waste pickers with capacity—analytic,administrative,and political— highest-efficiency gains.Advanced district energy state-of-the-art information and waste-to-energy to implement high-impact,cross-sector,cross-scale Systems that use energy cascading,exchange,and technologies can create hybrid solutions,illustrated, solutions.Some cities have created sustainability storage across industries,power plants,buildings, for example, by India's recently revised solid offices that are empowered to convene multiple transportation,water,solid waste management, waste management regulations(17). city departments,and many are leveraging multi and renewable energy production offer tremendous 6)Apply transboundary systems analysis to in- level and cross-national policy-exchange networks potential (15). Knowledge of urban morphol- form decisions about localized versus larger-scale (18).With the smart city agenda requiring high - ogy,combined with temporal and spatial cross- infrastructure.Driven by goals of local self-reliance, technology expertise,greater involvement of the sectoral infrastructure data,is essential. efficacy,and anticipated health and well-being private sector in infrastructure delivery is in- 4)Recognize diverse strategies for resource benefits,cities are increasingly focusing on more evitable.Many cities are initiating public-private efficiency in different city types.A technology- localized infrastructures,such as rooftop and com- partnerships and/or special financing for smart- oriented view of smart cities can result in trans- munity solar installations,community-supported city development.These arrangements raise ques- lating high-efficiency solutions from one country urban farms,and apartment-scaled wastewater lions about ownership, equity, and governance or culture to another,where they may not work treatment plants.Improved information about (19).It is equally important to ask where all the as well.For example,although tightly insulated, transboundary environmental footprints and local information that enables a smart, sustainable, highly instrumented,all-day centrally cooled and well being impacts are critical to clarify synergies and healthy city will reside.Transparent and adapt- heated buildings may be energy-efficient for the and trade-offs between local versus larger-scale ive governance arrangements that are open to United States and the European Union,the same infrastructure networks. public input and scientific study will empower approach may not translate to the more vernacular 7) Recognize coevolution of infrastructures cities,and the world,to learn by doing. architecture and informal user practices of Chinese and institutions(15).Matching the scale of en- These eight principles focus attention on higher- apartments,which tend to be spot-cooled over gineered infrastructures with that of the institutions order,systems-level decisions that society must 942 20 MAY 2or6•VOL 352 ISSUE 6288 sciencemag.org SCIENCE make to transition toward a smart,sustainable, PERSPECTIVE and healthy urban future.To achieve the full po- tential of smart cities, discussions must move beyond data to envision cities as multisectoral, Hidden linkages between multiscalar,social-ecological-infrastructural sys- tems with diverse actors,priorities,and solutions. 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R.G.Hollands,City 12,303-320(2008). global urban footprint expanded by 58,000 km thermore,the loss of agricultural land may result 20.Intergovernmental Panel on Climate Change,Climate Change (1).By 2030,built-up areas are forecasted to nearly in the need to expand crop production into mar- 2014:Mitigation of Climate Change.Contribution of Working triple in size over the 2000 area,an increase of ginal and fragile lands,as well as other ecosystems. Group IN to the Fifth Assessment Report of the 1.2 million km2(2).However,croplands,which In the tropics, deforestation due to agricultural Intergovernmental Panel on Climate Change,0.Edenhofer et at, account for 12%ofthe world's ice-free land cover, land expansion is estimated at 12 million ha per Eds.(Cambridge Univ.Press,2014). 21.AQUASTAT,Food and Agriculture Organization,"Water uses:' exceed urban areas,which take up less than 3% year(8).Notwithstanding these qualifications,the 2016;www.fao.org/nr/water/aquastaUwater_use/index.stm). (3).Though this difference in total area suggests effect of urban expansion on farmland loss is 22.International Energy Agency,"Water for energy;'2016; that expansion of urban areas will have a mini- unlikely to be the most important influence of www,worldenergyoutlook.org/resources/water- mal effect On Earth's total cropland,two quali- urbanization on food systems. energynexus/. 23.WHO,Global Status Report on Road Safety 2013:Supporting a ficatioris are important. On the demand Side, it is well documented Decade of Action(WHO,2013);www.who.inbviolence_injury- First,because built-up areas are growing faster that the diets of urban and higher-income so- prevention/road_safety_status/zo13/en/. than urban populations in most parts of the cieties require costly expenditures ofland,water, ACKNOWLEDGMENTS world(1,4),cropland loss is likely to be acute in and energy(9,10).With few exceptions,highly ur- The authors are grateful for support from NSF countries where urban population growth rates banized countries Consume more animal protein- (Partnership for International Research and Education are high and the,economy is largely agrarian. in the form of pork, poultry, beef, and dairy award 1243535 and Sustainability Research Thus,the loss of cropland due to urban expan- products-than the world average.Globally,the Networks award 1444745)and from the U.S.Agency Sion is likely to be more Of a regional problem average meat consumption per capita is 36.9 kg for International Development and the National Academy n here is huge variation between of Sciences(Partnership for Enhanced Engagement per year,butt g in Research subgrant 2000002841).The principles outlined 'Yale School of Forestry and Environmental Studies,Yale Countries, with higher-income Countries con- here were discussed at a workshop convened by ICLEI-South University,New Haven,CT 06511,USA.'Liu Institute for Global suming 81.8 kg per year per capita compared Asia and the University of Minnesota in January 2016, Issues and Institute for Resources,Environment and with 17.2 kg per year in lower-income countries which was attended by more than 40 city officials and policy-makers Sustainability,The University of British Columbia,Vancouver, (9)•In the United States,where 81%of the pop- from the United States,China,and India. British Columbia V6T 22,Canada. *Corresponding author.Email:karen.seto@yale.edu(K.C.S.); nlation lives in Urban areas,per-capita meat con - *Corresponding navin.ramankutty@ube.ca(N.R.) sumption is 89.7kg per year.In China,per-Capita, SCIENCE sciencemag.org 20 MAY 2016•VOL 352 ISSUE 6288 943 SPECIAL SECTION URBAN PLANET meat consumption quadrupled between 1970 Urbanization could drive profound changes and 2015,a period when the urban population in food systems in ways unrelated to rises in increased from 17.4 to 55.6%.Other countries "We need to moue beyond high rates of urbanization are under- � income, such as through shifts in norms and experiencingu�tderst Urbanization'S attitudes about food; increasing opportunity going similar dietary transitions(11,12).It is im- an(fi'a cost of time and the necessity of convenience; portant to point out that changes in diet are not dirat effects On diet and growing availability and access to modern en- limited to increased meat consumption but also toward exallllnlllg its ergy, and changes in the structure of the eco- include more nuanced shifts in quality,compo- nomy,household dynamics,the workforce,and sition,and sources of caloric intake.In general Zndim t effects on mom urban form and infrastructure(FYg.1).The pace changes in diet can be characterized as a shift use and the environment, of life in cities is fast, and with the onset of from complex carbohydrates,grains,vegetables, SUCK (IS embodied ener>�f Or the 24-hour workday and more women join- and fruits to a higher proportion of animal pro- ing the workforce,there is a growing need to teins,refined fats,refined sugars,alcohols,and food production, tnuuport, reduce meal cooking time. This creates a de- oils(13). paten mand for time-saving food preparation, from The exact mechanisms that undergird these `""�` St0 e, and dietary shifts are not well understood,and many the rest of the entire chain prepackaged items to reduced shopping time; meals away from home;and convenience foods studies conflate urbanization,rises in income, from farm to fork." on the go(14,15).Around the world,more ur- and westernization.More affluent households banized societies eat more meals away from can afford higher-quality diets with greater var- home(Fig.2).Urban and food systems coevolve: iety,the means to physically reach grocery stores large mega-urban regions affect our exposure Increased convenience allows people to work that have better selection,and nutritional knowl- and access to foods, as well as our food pre- longer,furthering the demand for convenient edge. Disentangling the income or economic ferences and choices?How does urban living foods.Although these foods reduce meal prep- development effect from the urban effect on influence our exposure to"foodstyles,"such as aration time,they also increase the need for pre- diets will require substantially more research veganism,organic,and local foods,as well as processing,packaging,and refrigeration.In 2005, that goes beyond comparison of urban diets to our purchasing habits and diets?We need to food container and packaging waste accounted rural ones.Given that urbanization is a major move beyond understanding urbanization's for nearly one-third of total municipal solid waste global trend,we need research that helps us direct effects on diet and toward examining in the United States(16). isolate the urban effects on diet.For example, its indirect effects on resource use and the In addition to packaging waste,food losses how does urban spatial form affect food de- environment, such as embodied energy for and waste place enormous burdens on the en- mand? How are our food choices shaped by food production,transport,packaging,cold stor- vironment by contributing to greenhouse gas where we live and work,their relative locations, age,and the rest of the entire chain from farm emissions,eutrophication,and the waste of re- and our travel behavior? How does living in to fork. sources used to produce food that is not eaten Urbanization&food systems Urbanization Research Food systems Built up area expansion————— � Loss of Land use& Separation of uses agricultural land (work from home) g _�aProduction built environment Travel modes Food loss Land use planning Convenientfoods More people Processing&packaging Household& 0 demography Packaging More diverse tastes - Economy&development Supermarkets Income———---—— _ Distribution&retail Cold chain 9 I Opportunity cost of time Diet composition Lifest le&culture Food waste Work away from home Consumption Food away from home New technologies Food safet Innovation y Exposure to ideas A——Established links -1 Unexplored linkages Fig. 1. Established and underexplored linkages between urbanization and food systems.The underexplored linkages are illustrative and not exhaustive. 944 20 MAY2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE 100 ® ej•-• estimated 500 million smallholder farms in de- • • ®• veloping countries providing livelihoods for almost • • 2 billion people(21).Urban expansion may dis- • ��$ j 80 : •� •• place these farmers into marginal lands,and the •,1• d• • • •e• • •• increase in land value may encourage them to • • sell their farms and seek alternate means of 0 s livelihood,possibly in urban areas,leading to 60 0-0- 0 ® ® ® even greater rural-to-urban migration.Further, 0 •• •� ®® ®® as cities grow larger,the food retail market be- CL c ® ® ® comes increasingly dominated by large super- 40 • ® market chains, and this has secondary effects • ® on traditional retailers,small-scale producers, ® traditional food brokers,and the entire supply 20 chain(22). Most discussions of food security focus on how to sustainably provide for a world of 9 to 0 10 billion people in 2050.Much less attention F} 0 20 40 60 80 100 has been paid to the fact that -6.5 billion of %Food consumed away from home these people will live in urban areas and that the transformation toward a more urbanized Fig.2. Percentage of the national population living in urban areas versus percentage of con- society will have many consequences for food Sumer expenditures on food consumed away from home for 86 countries in 2014. Urban systems.The overwhelming effects will be in- population estimates are from the World Bank;estimates for shares of food consumed at home are direct. To achieve food security in the urban from the Economic Research Service of the U.S. Department of Agriculture (we inferred the century,we urgently need more research that percentage of food consumed away from home to be 100%minus the percentage of food consumed unravels how these two systems are linked, at home). REFERENCES (1).Food loss and waste within the food system Where they exist, urban planning and land- 1. K.C.Seto,M.Fragkias,B.Goneralp,M.K.Reilly,PLOS ONE 6, depend on many factors,but the level of econom- use zoning regulations greatly affect food retail e23777(2011). 2. K.C.Seto,B.GUneralp,L.R.Hutyra,Proc.Natl.Acad.sci.U.S.A.is development is a strong predictor: Precon- diversity and accessibility. Transport planning, 109,16093-16088(2012). Sumer food losses within the supply chain are modes of mobility,street connectivity,and land- 3. N.Ramankutty,A.T.Evan,C.Monfreda,J.A.Foley,Global more prevalent in developing countries,whereas use mix affect how often,people shop for food, siogeochem.Cycles 22,GB1003(2008). V postconsumer food waste is a bigger issue in what they buy, and where they eat. In cities 4. S.Angel,J.Parent,D.L.Civco,A.Blei,D.Potere,Prog.Plann. high-income countries(18).Urbanization may where street connectivity is high-characterized 75,53-107(20 5. F.Martellozzo etf a. al.,Reg.Environ.Change 15,881-893 actually be beneficial for reducing food losses by smaller blocks, shorter distances, and many (2015). I; through improvements in technology,such as intersections-there is apositive correlation with 6. H.C.J.Godfray et al.,Philos.Trans.R.Soc.London Sec 8 365, cold storage and transportation.There are many walking and, thus, more convenience, higher 2769-2777(2010). reasons why people in the developed world waste accessibility,and lower energy costs of food pro 7. J.A.Foley et al.,Nature 478,337-342(2011). 8. E.B.Barbier,Am.J.Agric.Econ.86,1347-1353(2004). so much food:We overbuy and then overprepare curement. Land-use regulations are central to 9. A.J.McMichael,J.W.Powles,C.D.Butler,R.Uauy,Lancet and discard excess food.This is overwhelmingly a creating retail"foodscapes"that are diverse by ei- 370,1253-1263(2007). problem of the affluent, where food is a small ther enabling small-scale,independent food shops 10.B.M.Popkin,World Dev.27,1905-1916(1999). percentage of the total household budget, thus and restaurants or limiting food commerce to 11. P.M.Poi,Food Policy 3 u r 133(8 ppl.2). p � 12. B.M.Popkin,S.Du,J.Nutr.133(suppl.2),3898S-3906S reducing the cost of discarding food. Again, as stores or chains that can afford higher rents and (2003). with diets,disentangling the income effect from fill large retail spaces. 13. D.Tilman,M.Clark,Nature 515,518-522(2014). 14. J.F.Guthrie,B.-H.Lin,E.Frazee,J.Nutr.Educ.Behan.34, the urban effect on food loss and waste will re- Urban areas are also hubs of innovation,where 140-150(2002). quire far more research.For example,how much new technologies and ideas about food systems 15. H.Ma,J.Huang,F.Fuller,S.Rozelle,Can.J.Agric.Econ.54, does food consumed away from home,which is emerge,such as vertical farming,entomophagy, 101-119(2006). strongly associated with urban living, influence the slow food movement,farmers markets,and 16. K.Marsh,B.Bugusu,J.Food Scf.72,R39-1355(2007). food waste?How do mixed-use urban forms,with community-supported agriculture. Urban dwel v. M.Kummu et at.,sci.Total Environ.a3s,477-489 (2012). close access to grocery stores, allow people to lers are increasingly disconnected from the agn- 18.J.Aschemann-Witzel,Science 352,408-409(2016). purchase food when they need it and reduce cultural land base but are finding creative ways 19. R.D.Garrett,X.Rueda,E.F.Lambin,Environ.Res.Lett.8, household food waste? to remain connected to the food system.Changes 044055(2013). 20.H.Willer,L.Kilcher,Eds.,"The World of Organic Agriculture: With greater numbers of people and activities, in urban consumer preferences can have far- Statistics and Emerging Trends 2011"[International urban areas also require more institutions to reaching consequences. For example, Euro- Foundation for Organic Agriculture Movements and maintain law and order,sanitation, and public pean preferences for non-genetically modified Research Institute of Organic Agriculture(FiBL),20111; hygiene.More rules and changes in attitudes come foods have contributed to the rapid expansion http://orgprihts.org/19310/l/world-of-organic-agriculture- together to create new norms and regulations of South American farming and the develop- 2011.pdt. 21. High Level Panel of Experts on Food Security and about food safety.Though some of these regula- ment of entirely new supply chains (19). The Nutrition(HLPE),"Investing in smallholder agriculture tions (such as cold-storage requirements) may rapid growth of organic farming is driven by for food security.A report by the High Level Panel appear benign,together they constitute a sub- increasing demand from urban consumers in of Experts on Food Security and Nutrition of the stantial shift in where and how food is stored, North America.and Europe,whereas the major- Committee on World Food security"(Food and Agriculture Organization of the United Nations,2013); packaged, and sold. In many Asian cities, wet ity of organic farmers are located in developing vnvw.fao.org/fileadmin/user_upload/hlpe/hlpe-documents/ markets are giving way to more sanitized farm- countries(20). HLPE_Reports/HLPE-Report-6_Investing_in_smallholder- ers markets and multinational supermarkets, Of all the myriad ways in which urbaniza- agriculture.pdf. parts Of the food system, 22•T.Reardon,C.P.Timmer,C.B.Barrett,J.Berdegue,Am.J. erns about the avian flu but tion affects different a partly due to concerns b P1140-1146(2003). Agric.Econ.85 also because of changing attitudes around fresh- the effects on the people who produce food are ( ) ness and modernity. perhaps some of the least studied.There are an 10.1126/science.aaf7439 SCIENCE sciencenmg.org 20 MAY 2016•VOL 352 ISSUE 6288 945 SPECIAL SECTION URBAN PLANET PERSPECTIVE main sources of inefficiency in the dynamics of city development.One arises from the difficulty of forming expectations;for example,pessimism Building functional cities about future city growth undermines willingness to invest and leads to a lower,more sprawling J.Vernon Henderson,'*Anthony J.Venables,'°2 Tanner Regan,'Ilia Samsonov' city. The other is institutional obstacles in the process of converting slum developments to The literature views many African cities as dysfunctional with a hodgepodge of land uses and formal sector usage. poor"connectivity."One driver of inefficient land uses is construction decisions for highly There are many such institutional obstacles. durable buildings made under weak institutions.In a novel a Formal sector development requires financing g approach, model the dynamics of urban land use with both formal and slum dwellings and ongoinngg urban and enforcement of contracts,which in turnan redevelopment to requires land ownership rights to be formalized higher building heights in the formal sector as a city grows.We analyze the evolution of Nairobi to mitigate the risk of expropriation.Land rights using a unique high—spatial resolution data set.The analysis suggests insufficient building often unclear because of coexisting systems volume through most of the city and large slum areas with low housing volumes near the center, are are often ate ownership(some illegal or quasi-legal), where corrupted institutions deter conversion to formal sector usage. ofpricommunal ownership, and government owner- ship. Competing claims may result in lengthy ost cities in the developed world use lived,and construction decisions(such as build- court cases.Slum areas are particularly complex, land in an orderly pattern that allows ing height)are based on expectations of future with"planning or regulatory powers...split be- cities to achieve high productivity.For rents;and informal,or slum settlement,where tween a galaxy of private sector actors,landlords, example,businesses mainly reside in a construction is flexible or adjustable over time chiefs and bureaucrats, and gangs" (9). Land central business district(CBD), and re- (e.g.,through use of corrugated iron sheets),build- administration is subject to corruption. The sidential neighborhoods have regular layouts ing a single story is cheap,but building high is Kenyan elite has been guilty of land-grabbing, with high densities near the center and lower very expensive.This distinction is illustrated in with a government inquiry alleging that the densities further out(I).In contrast,many cities Nairobi,where 57%of slum dwellings are made of land allocation process has been subject to cor- in developing nations have office towers bordered sheet metal and 15%of mud and wood,whereas rupt and fraudulent practices and"outright plun- by slums, scattered fringe developments, and a 90%of formal residences are made of stone,brick, der"(I0).As a result,the cost and feasibility of consequent lack of connectivity between firms, or cement block(8). conversion to legal formal usage varies depend- workers,and consumers.Such cities are viewed as In the efficient outcome in the model,slums ing on a ploys history;plots with high conversion nonfunctional(2),with large numbers of people form at the edge of the city,where land is cheap. costs remain informal much longer.A spatial in informal settlements[62%of the African urban As the city grows, old slums are converted to jumble of land rights and conversion costs re- population according to(3)],poor transport infra- formal settlement and new ones form on the ex- sults in a hodgepodge of uses,land-use inten- structure and limited ability to commute(4),and panding edge.Formal sector development is sub- sities, and stages of redevelopment throughout low worker productivity(5). ject to periodic demolition and reconstruction, the city,including close to the center. Here, we explore factors that may underlie and structures become successively taller and Studying these inefficiencies requires data on nonfunctionality of many cities in the developing denser as the city grows and land values increase. individual buildings and the ability to track them world. We analyze how construction decisions If slum housing is inherently of lower quality, through time to quantify the potential loss of made under weak and corrupt institutions can be then slums will eventually be phased out entirely building space.Such data are generally difficult a driver of nonfunctionality.The built environ- as incomes grow,just as 19th-century tenements to obtain. For our Nairobi study, we used a ment resulting from these decisions accounts for and shacks in London and New York disap- building footprint data set based on extremely two-thirds of produced capital in developing peared decades ago.Our model Q)analyzes two high-resolution aerial photos(well under 50-cm countries(6)and is long lived.As such,weak institutions undermine the competitiveness of cities,and thus,bad decisions made today have s effects that last for generations.We first dis- cuss recent model results and then use Nairobi, Slum Formal Kenya—a city of about 5 million people that is KI heC s " ' ' growing at a rate of 3 to 4%per year—to map out 2 21 49 how the built environment has cha nged and to ��.�� 18' 139 explore ways in which it appears to deviate from r 15 32 an efficient pattern, with insufficient build' p > mg r a t` � volume through most of the city. . 13 25 In a recent study (hereafter referred to as it 20 HRV)(7),we developed a general model of the x � dynamics of economically efficient urban land 9 16 use and of key elements that impede efficient r urban development. To do so, we adapted a 7 12 t standard urban model to a growth context and 5 ,9 the circumstances of developing countries.The `� t� 3 6 model captures rapid population growth and two types of housing technology:Formal hous Average height(m) ing,in which capital is sunk,buildings are long- Fig.1.City of Nairobi building height and distribution.Nairobi shows average built height in 2015 as 150-m by 150-m cells split across the formal and slum sectors.The compass (top left) points I north.The location of the Kibera slum and the CBD are marked.The boundary of the city spans about London School of Economics and Political Science,London 22 km east to west and 11 km north to south;the map tilt may distort the appearance of distances. WC2A 2AE,UK.2Department of Economics,Oxford University,Oxford OX13UQ,UK. Modified from HRV. [Background imagery Airbus Defense and Space 2016,taken from the SPOT5 *Corresponding author.Email;j.v.henderson@lse.ac.uk satellite 20 September 20041. 946 20 MAY 2016•VOL 352 ISSUE 6288 sciencemag.org SCIENCE k resolution),which allows 0 6 Net change In summary, Nai- clear demarcation even robi has many of the of buildings in slums, features of a"normal" satellite data to derive 0.4 Net redeveloped city:High buildings in Infill road coverage,and LIDAR the CBD and declining data for building heights 0.3 heights and land prices (7).We used city studies to away from the center. that mapped slums in 0.2 � � Yet there is substan- G 2003-04(11)and slums c tial evidence of inef and ownership or land > 01 ficient land-use. The rights in 2012(12).For the Demolished low-volume intensity �.F later time period,house of slums and the per- 0 ------------------------------------------------------ ----------------------------- and land prices are avail- sistence of slums rel- able from surveys or I atively dose to the center scraping the Web.We 0 2 4 6 8 lead to a substantial developed novel methods Distance to center(km) loss of housing capacity. to integrate and analyze Fig.2.City of Nairobi volume change by sector since 2004.Formal sector volume change from We argue that such per these data,including over- 2004 to 2015 as a fraction of initial volume by distance.The ratio of net volume to initial volume is sistence is due to the f laying building footprints broken down into change due to infill redevelopment and demolition as defined in HRV.This sample myriad of institutional of the city at different excludes cells that had no buildings in both 2015 and 2004, Modified from HRV. and political obstacles points in time to define to redevelopment. infill,reconstruction,demolition,and no change. replaced)as a fraction of initial volume(Fig.2). Although the data are specific to Nairobi,the As can be seen in the three-dimensional map In the 0-to 1-km ring at the CBD,use is locked in modeling and analysis are more general.Weak (Fig.1),building heights vary widely throughout by roads,colonial buildings,and tall complexes and corrupt land market institutions are com- Nairobi,reflecting formal and informal housing. built over the last 40 years.Total road area de- mon throughout much of Africa,which suggests ( The city is monocentrie,constrained by national clines sharply with distance from the center,as that aspects of our findings for Nairobi have parks to the north and south;undefined spaces modeled by Sclow and Vickrey(13).Between 1 and more general applicability. Whereas the focus within the city include an airport, golf course, 5 km,as the model suggests,there is substantial has been the built environment and much of data and the President's complex.Slums include the net redevelopment in the face of escalating land is a view from the sky,our continuing work com- 1000-acre slum of Yibera,to the south-west of prices,with new buildings taller than their older bines this with economic and population censuses the city center that we discuss below. neighbors. The volume of net redevelopment and surveys, in order to give detail for what is Land prices,as recorded in 2015,decline sharply peaks at 4 km out,where it amounts to just under happening to people and firms on the ground. with distance from the CBD.There are no slums in 30%of old volume.Beyond 5 km,volume changes Combining data sources and institutional de- the CBD, and the proportion of developed land are dominated by inflll, tails of specific cities will help inform urban policy occupied by slums peaks at 45%at a distance of What about slums?Up to about 2 km from the to improve functionality, as the African urban 5 km out from the CBD.In Nairobi,slums are CBD,slums are demolished and redeveloped.Be- population trebles over the next three decades. not concentrated at the edge(which,according yond that there is less redevelopment than might to the model,would be economically efficient), be expected.Why?In HRV,we argue that remain- REFERENCES although city mapping may underrepresent ing slums nearer the CBD,like Kibera,have high 1. G.Duranton,D.Puga,in Handbook of Regional and Urban emerging slums at the fringe.More to the point, costs of conversion to formal usage.Slum land near Economics,G.Duranton,J.V.Henderson,W.strange,Eds. slums appear in a scattered fashion throughout, the center,including Kibera,is government-owned (Elsevier,Philadelphia,2015),vol.5,pp.467-560. even near the CBD which indicates potentially 12—a code word for conflicting private claims, 2. S,Coulibafy et al.,"World development report 2009:Reshaping g> P Y ( ) P economic geography'(Report 43738,World Bank Group, important land market fictions.Building heights with the government having seized ownership Washington,DC,2008). in the formal sector average about 23 in in the but not responsibility.Slum landlords there make 3. United Nations Human Settlements Programme,State of CBD,in contrast to expectations that there would high profits and much of the land is controlled by the worlds'Cities 201212013.Prosperity of Cities tk (UN-HABITAT,Nairobi,Kenya,2012). be overall less height in Nairobi.Heights fall to political figures with a vested interest not to de- 4. Trans Africa Consortium,Public Transport in Sub-Saharan t about 6 to 7 in at a distance of 10 km from the velop the land;redevelopment would take away Africa:Major Trends and Case Studies[International j CBD.Slums have similar height throughout the their profits on land to which they have no legal Association of Public Transport(UITP),Brussels,20101. city and,at about 5 in,are less tall than formal claim.Nearer the fringe,land ownership in slums 5. M.Fay,C.Opal,"urbanization w thoutgrowth:snot-so-uncommon buildings,as modeled.Despite the lack of roads becomes increasingly private, phenomenon"(Policy Research Working paper series 2412, The World Bank,2010). and green space and the intense crowding of The constraint on slum redevelopment nearer 6. World Bank Group,where Is the wealth of Nations?:Measuring buildings in slums,height in the formal sector the center has significant welfare costs:There is Capital for the 21st Century(Report 34855,World Bank Group, trumps intense footprint coverage in slums,so lost volume of space due to not building high as Washington,DC,2005). that building volume (height x footprint) per we described above,and the quality of the built 7. J.V.Henderson,T.Regan,A.Venables,"Building the city:Sunk capital and sequencing"(Discussion paper 11211,Centre for unit land in slums is always lower than in for- space and unit rents are low compared with Economic Policy Research,London,2016). mal developments.An implication is that the those of the formal sector.We hypothesize that 8. C.Zinnes et al.,Kenya Urban Program Baseline Study(NORC, presence of slums near the CBD has a large im- slum landlords have invested little in land im- university of Chicago,Chicago,2012);www.norc.org/Research/ pact on building volume.At 2,3,and 4 km from provements,such as infrastructure and regular- Pro)ects/Pages/kenya urban-program baseline study.aspx 9. B.Marx,T.Stoker,T.Sud,J.Econ.Perspect.27,187-210(2013). the center,conversion of slums to formal usage ized lay-out near the center,because they cannot 10.R.Southall,Rev.Aft Polit.Econ.32,142-151(2005). would increase building volumes in those slum capture those returns when housing spaces are 11. S.Williams,E.Marcello,J.M.Klopp,Ann.Assoc.Am.Geogr areas by 148%,95%,and 53%,respectively,one redeveloped.A simple calculation (reported in 104,114-130(2014). ll land use. HVR suggests.that lack of redevelopment re- 12.World Bank,"Resettlement Action Plan report for KCC indication of potentially inefficient an P Y ) � P (Embakasi)Informal Settlement in Nairobi County"(Report Turning to dynamics,we determined the vol- duces land values in Mbera by the order of about RP1059,World Bank Group,Washington,DC,2014). ume of infill(new buildings where there were $1 billion. Such a magnitude of potential gain 13. R.M.Solow,W.S.Vickrey,J.Econ.Theory 3,430-447 none in 2004),net redevelopment(newbuilding from redevelopment indicates the potential for a (1971), where there had been an earlier structure),and political solution:to buyout the actors inhibiting 18 March 2016;accepted 26 April 2016 demolition (buildings demolished and not yet redevelopment and to help relocate tenants. 10.1126/science.aaf715o SCIENCE sciencemag.org - 20 MAY 2016•VOL 352 ISSUE 6288 947 a e Join one of the top naturalists Lloyd Esler to see x some of the most spectacular scenery in the world in s@gfallg ' New Zealand's national parks.From kiwis to kakas, " temperate rainforests to glacial valleys,New Zealand at�wa s In possesses a rich heritage.The geologic forces are as -Cacer,' • . dynamic as anywhere on earth,and can be seen in the fascinating geyserfields in Rotorua,in the plung ,� ing cliffs atMilfordd Sound,and the spectacular peaks and glaciers of the Southern Alps.$4,995pp+air Ce1/E?�O�J(Y12Clta� blotb Fora detailed brochure, call(800)252-4910 x All P per are prices person twin share+air • • s BETCHART EXPEDITIONS Inc. 17050 Montebello Rd,Cupertino,CA 95014 TO t'egtS@iCrt g0 �O: Email:AAASInfo@betchartexpeditions.com b►t tylSc�ec►ceW b�naEJune . .. www.betchaitexpe(litions.com i r Be Amongthe First to Publish in Science • • • cs F • ACCEPTING MANUSCRIPTS xv ScienceR • • • • Science Robotics is a unique journal created to help advance the research CII� c Robotics and development of robotics for all environments.Science Robotics will provide a much-needed central forum to share the latest technological WAAAS discoveries and to discuss the field's critical issues. 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