How slums can save the planet

Sixty million people in the developing world are leaving the countryside every year. The squatter cities that have emerged can teach us much about future urban living
January 27, 2010
Dharavi, Mumbai, where population density reaches 1m people per square mile

In 1983, architect Peter Calthorpe gave up on San Francisco, where he had tried and failed to organise neighbourhood communities, and moved to a houseboat in Sausalito, a town on the San Francisco Bay. He ended up on South 40 Dock, where I also live, part of a community of 400 houseboats and a place with the densest housing in California. Without trying, it was an intense, proud community, in which no one locked their doors. Calthorpe looked for the element of design magic that made it work, and concluded it was the dock itself and the density. Everyone who lived in the houseboats on South 40 Dock passed each other on foot daily, trundling to and from the parking lot on shore. All the residents knew each other’s faces and voices and cats. It was a community, Calthorpe decided, because it was walkable.

Building on that insight, Calthorpe became one of the founders of the new urbanism, along with Andrés Duany, Elizabeth Plater-Zyberk and others. In 1985 he introduced the concept of walkability in “Redefining Cities,” an article in the Whole Earth Review, an American counterculture magazine that focused on technology, community building and the environment. Since then, new urbanism has become the dominant force in city planning, promoting high density, mixed use, walkability, mass transit, eclectic design and regionalism. It drew one of its main ideas from the houseboat community.

There are plenty more ideas to be discovered in the squatter cities of the developing world, the conurbations made up of people who do not legally occupy the land they live on—more commonly known as slums. One billion people live in these cities and, according to the UN, this number will double in the next 25 years. There are thousands of them and their mainly young populations test out new ideas unfettered by law or tradition. Alleyways in squatter cities, for example, are a dense interplay of retail and services—one-chair barbershops and three-seat bars interspersed with the clothes racks and fruit tables. One proposal is to use these as a model for shopping areas. “Allow the informal sector to take over downtown areas after 6pm,” suggests Jaime Lerner, the former mayor of Curitiba, Brazil. “That will inject life into the city.”

The reversal of opinion about fast-growing cities, previously considered bad news, began with The Challenge of Slums, a 2003 UN-Habitat report. The book’s optimism derived from its groundbreaking fieldwork: 37 case studies in slums worldwide. Instead of just compiling numbers and filtering them through theory, researchers hung out in the slums and talked to people. They came back with an unexpected observation: “Cities are so much more successful in promoting new forms of income generation, and it is so much cheaper to provide services in urban areas, that some experts have actually suggested that the only realistic poverty reduction strategy is to get as many people as possible to move to the city.”

The magic of squatter cities is that they are improved steadily and gradually by their residents. To a planner’s eye, these cities look chaotic. I trained as a biologist and to my eye, they look organic. Squatter cities are also unexpectedly green. They have maximum density—1m people per square mile in some areas of Mumbai—and have minimum energy and material use. People get around by foot, bicycle, rickshaw, or the universal shared taxi.

Not everything is efficient in the slums, though. In the Brazilian favelas where electricity is stolen and therefore free, people leave their lights on all day. But in most slums recycling is literally a way of life. The Dharavi slum in Mumbai has 400 recycling units and 30,000 ragpickers. Six thousand tons of rubbish are sorted every day. In 2007, the Economist reported that in Vietnam and Mozambique, “Waves of gleaners sift the sweepings of Hanoi’s streets, just as Mozambiquan children pick over the rubbish of Maputo’s main tip. Every city in Asia and Latin America has an industry based on gathering up old cardboard boxes.” There’s even a book on the subject: The World’s Scavengers (2007) by Martin Medina. Lagos, Nigeria, widely considered the world’s most chaotic city, has an environment day on the last Saturday of every month. From 7am to 10am nobody drives, and the city tidies itself up.

In his 1985 article, Calthorpe made a statement that still jars with most people: “The city is the most environmentally benign form of human settlement. Each city dweller consumes less land, less energy, less water, and produces less pollution than his counterpart in settlements of lower densities.” “Green Manhattan” was the inflammatory title of a 2004 New Yorker article by David Owen. “By the most significant measures,” he wrote, “New York is the greenest community in the United States, and one of the greenest cities in the world…The key to New York’s relative environmental benignity is its extreme compactness. Manhattan’s population density is more than 800 times that of the nation as a whole. Placing one and a half million people on a twenty-three-square-mile island sharply reduces their opportunities to be wasteful.” He went on to note that this very compactness forces people to live in the world’s most energy-efficient apartment buildings.

The idea of measuring environmental impact in notional acres was first introduced by Mathis Wackernagel and William Rees in Our Ecological Footprint (1996) as a way to estimate the resource efficiency of cities and to condemn suburban sprawl. The concept has been very useful in shaming cities into better environmental behaviour, but comparable studies have yet to be made of rural populations, whose environmental impact per person is much higher than city dwellers. Nor has footprint analysis yet been properly applied to urban squatters and slum dwellers, which score as the greenest of all.

Urban density allows half of humanity to live on 2.8 per cent of the land. Demographers expect developing countries to stabilise at 80 per cent urban, as nearly all developed countries have. On that basis, 80 per cent of humanity may live on 3 per cent of the land by 2050. Consider just the infrastructure efficiencies. According to a 2004 UN report: “The concentration of population and enterprises in urban areas greatly reduces the unit cost of piped water, sewers, drains, roads, electricity, garbage collection, transport, health care, and schools.” In the developed world, cities are green because they cut energy use; in the developing world, their greenness lies in how they take the pressure off rural waste.

The Last Forest (2007), a book by Mark London and Brian Kelly on the crisis in the Amazon rainforest, suggests that the nationally subsidised city of Manaus in northern Brazil “answers the question” of how to stop deforestation: give people decent jobs. Then they can afford houses, and gain security. One hundred thousand people who would otherwise be deforesting the jungle around Manaus are now prospering in town making such things as mobile phones and televisions.

The point is clear: environmentalists have yet to seize the opportunity offered by urbanisation. Two major campaigns should be mounted: one to protect the newly-emptied countryside, the other to green the hell out of the growing cities.


More than any other political entity, cities learn from each other. News of best practices spreads fast. Mayors travel, cruising for ideas in the cities deemed the world’s greenest—from Reykjavik to Portland, Oregon, and my hometown of San Francisco. But what we need is a new profession of active urban ecology, which figures out how to fix the problems of urban living (cockroach predation, waste from markets or sanitation, a persistent cause of disease in slums) and helps cities engage natural infrastructure (rivers and coastlines play a role similar to highways and sewer lines) with the same level of sophistication brought to built infrastructure.

One idea that could be transferred from squatter cities is urban farming. An article by Gretchen Vogel in Science in 2008 enthused: “In a high-tech answer to the ‘local food’ movement, some experts want to transport the whole farm shoots, roots, and all to the city. They predict that future cities could grow most of their food inside city limits, in ultraefficient greenhouses… A farm on one city block could feed 50,000 people with vegetables, fruit, eggs, and meat. Upper floors would grow hydroponic crops; lower floors would house chickens and fish that consume plant waste.”

Urban roofs offer no end of opportunities for energy saving and “reconciliation ecology.” Planting a green roof with its own ecological community is well-established. For food, add an “ultraefficient greenhouse”; for extra power, add solar collectors. And the most dramatic gains can come from simply making everything white. According to a 2008 study from the Lawrence Berkeley National Laboratory in California, if the world’s 100 largest cities replaced their dark roofs in this way, it could offset 44 metric gigatonnes of greenhouse gases.

Some environmentalists already are proponents of urban compactness. New zoning rules can be used to allow people to live and work closer together. Taxes can cut car use. Child-friendly policies and subsidised housing could bring down the high cost of city centre living, which drives families to the suburbs (and good schools follow them). Finally, it is better infrastructure that makes cities possible—so what would infrastructure rethought in green terms look like? Some of it will surely look like the new mass transit systems being built in China, or the high-speed rail that is finally coming to the US. And all of this should be powered by smart and micro grids—allowing local generation and the distribution of electricity. The new generation of small, modular nuclear reactors being developed in the US and elsewhere, which provide less than 125 megawatts and are built offsite, could have an important role.

Of course, fast-growing cities are far from an unmitigated good. They concentrate crime, pollution, disease and injustice as much as business, innovation, education and entertainment. The recent earthquake in Haiti demonstrates the danger of slum buildings. But if they are overall a net good for those who move there, it is because cities offer more than just jobs. They are transformative: in the slums, as well as the office towers and leafy suburbs, the progress is from hick to metropolitan to cosmopolitan, and with it everything the dictionary says that cosmopolitan means: multicultural, multiracial, global, worldly-wise, well travelled, experienced, unprovincial, cultivated, cultured, sophisticated, suave, urbane.

And just as this was true during the industrial revolution, so the take-off of cities will be the dominant economic event of the first half of this century too. It will involve huge infrastructural stresses on energy and food supply. Vast numbers of people will begin climbing the energy ladder from smoky firewood and dung cooking fires to diesel-driven generators for charging batteries, then to 24/7 grid electricity. They are also climbing the food ladder, from subsistence farms to cash crops of staples like rice, corn, wheat and soy to meat—and doing so in a global marketplace. Environmentalists who try to talk people out of it will find the effort works about as well as trying to convince them to stay in their villages. Peasant life is over, unless catastrophic climate change drives us back to it. For humanity, the green city is our future.


In Bangkok’s slums, most homes have a colour television—the average number is 1.6 per household. Almost all have fridges, and two-thirds have a CD player, washing machine and a mobile phone. Half of them have a home telephone, video player and motorcycle. (From research for UN report The Challenge of Slums.)

Residents of Rio’s favelas are more likely to have computers and microwaves than the city’s middle classes (Janice Perlman, author of The Myth of Marginality.)

In the slums of Medellín, Colombia, people raise pigs on the third-floor roofs and grow vegetables in used bleach bottles hung from windowsills. (Ethan Zuckerman, Berkman Center for Internet and Society at Harvard Law School.)

The 4bn people at the base of the economic pyramid—all those with [annual] incomes below $3,000 in local purchasing power—live in relative poverty. Their incomes… are less than $3.35 a day in Brazil, $2.11 in China, $1.89 in Ghana, and $1.56 in India. Yet they have substantial purchasing power... [and] constitute a $5 trillion global consumer market.

(The Next 4 Billion, Allen L Hammond et al.)


Stewart Brand is one of the world’s most influential—and controversial—environmentalists. After graduating in biology from Stanford University, California, in 1960, he became involved with the hippy movement and writer Ken Kesey’s “merry pranksters,” who were the subject of Tom Wolfe’s book The Electric Kool-aid Acid Test. Brand’s hugely influential Whole Earth Catalog, a counterculture guide to self-sustainable, communal living, was published between 1968 and 1972, and occasionally thereafter until 1998.

Co-founder of The Long Now Foundation and the Global Business Network, Brand lives on a houseboat in San Francisco Bay.

His new book, Whole Earth Discipline (Atlantic Books), challenges many of the long-held opinions of the environmental movement.