Cities appeared relatively late in human history, and have gradually evolved over five millennia to support complex economic, political, religious, academic and military organizations and hierarchies. However, their concentration of wealth, talent and creativity that breeds cultural and scientific innovation also fosters dereliction and decay.
This has given rise to the emerging field of urban ecology, which regards the reform of these "ecosystems" as no less than the key to the planet's future. Bringing together architects, academics, planners, politicians and civil society, the movement has begun creating greener, fairer urban alternatives on every continent of the world.
For anyone skeptical of the urgent need for action in this area, a few fascinating facts may not go amiss.
For instance, in 1900 just 15 percent of the world's population lived in cities; today's figure is 50 percent, and by 2025 it is expected to be 60 percent. However, this transition has unleashed far-reaching social and environmental woes, since, for example, although cities occupy a mere 2.5 percent of the earth's surface, they consume 75 percent of its resources and produce most of its waste.
In 1990, moreover, there were 12 megacities (with populations of 10 million or more) -- today there are 20, mostly in the debt-ridden developing world where housing and services such as water and sanitation can't keep up with demand. Pollution, squalor, disease and exploitation are worsening in such centers as corporations shift production there to avail themselves of cheaper labor and looser environmental restrictions. The last three decades have also seen human tides of squatters driven to the cities from rural regions degraded by overfishing, agribusiness, clear-cut logging or armed conflict. In Monrovia, capital of Liberia, for instance, 42 percent of the population are squatters. In Mumbai, India, and elsewhere, squatter settlements are periodically razed by authorities, often to make room for commercial development.
To reverse these trends, some urban ecologists are creating more holistic definitions of urban health that take account of environmental or social costs neglected by traditional measures of "progress." University of British Columbia professor William Rees' groundbreaking "ecological footprint" of cities measures urban consumption and waste in terms of surface area. London, for example, requires all the U.K.'s productive land to support its consumption and absorb its waste -- an area 125 times its size.
While there is no single formula for the ideal "ecocity," it would certainly include a vigorous local democracy, a sense of community, high density, green areas, wildlife corridors, efficient recycling and renewable energy, bike and pedestrian paths, and good public transportation.
On average, automobile-related space occupies a third of urban areas, so that a sprawling, car-era city like Los Angeles occupies three times the area of comparably populated, longer-established New York City. However, car-dependent zoning of suburban residential areas from workplaces and shops cuts ever deeper into animal habitats, and also reduces opportunities for human interaction. A symbol of "progress" in newly industrializing countries, cars appear to promote "independence" -- despite the fact that suburbanites must then depend on them for even basic errands.
As a result, a resident of a typically high-density Dutch city produces half the carbon dioxide of the average resident of a typically low-density Canadian city. Now, with urban ecology in mind, some municipalities are recreating aspects of older, more compact European and Asian cities through car-free zones, mixed residential and commercial areas, town squares and parks. Some have also begun limiting their growth by statute, as well as improved public transportation and creating bike trails and walking paths.
Of course buildings play a central role in urban energy consumption, and the creation -- or destruction -- of a sense of space and beauty. So-called climate-responsive architecture works with local conditions to design buildings with southern exposure and terraces to maximize sunlight and the potential for solar-power generation. Local or recycled materials, such as mud, clay, stone, straw or even animal dung can also reduce the demand for imported natural resources and express a unique regional identity.
In Adelaide, Australia, for example, formerly run-down Whitmore Square is being redesigned as blocks of ecological housing built with adobe and straw bale, with on-site water recycling, community gardens and revegetation projects.
One of the biggest and fastest-growing urban demands on nature is for food -- much of it transported long distances after being produced by agribusiness methods that result in chemical runoff, soil erosion, water mining and the burning of fossil fuels. While even the most idealistic urban ecologist would likely not imagine large cities becoming self-sufficient in food, urban agriculture is one way to revitalize local economies, take pressure off farmland, and reduce the "heat-island" effect.
Until recently, a Belgium-sized area of land produced grain, poultry, fish (mainly carp) and vegetables for Beijing's inhabitants using human and animal waste. But in the rush to modernize, China is replacing city farmland with concrete, and importing more food than ever. Conversely, whereas urban agriculture was outlawed under apartheid to control land rights, today in South Africa it is supported and flourishes in the squatter settlements.
In fact, around the world, a wealth of schemes to improve cities are coming from government initiatives as well as the grassroots -- from rooftop greenery in Japan, to rainwater harvesting in India, community banking initiatives in South Africa and city gardens in vacant lots of New York City.
According to Jari Niemela, professor of urban ecology at the University of Helsinki, experts from both developing and industrialized regions have much to share, despite obvious differences. "Third-world priorities are more human-oriented," he explains in an e-mail interview. "Their first goal is to make urban areas better places for people, for example, more pleasant or safer. In industrialized countries, there's more emphasis on urban green diversity and aesthetic values. But there's lots of common ground."
Niemela cited one of the more successful sustainable cities as being Curitiba in Brazil, which has an efficient public transport system and denser development along its bus routes. Twenty-six parks, linked by bicycle paths, double as flood-retention beds. "Lighthouses of knowledge" -- public libraries housed in brightly-colored towers -- have also been set up for children to wait for working parents after school hours. In Curitiba, too, he said that 70 percent of municipal trash is recycled or composted, and a "green-exchange program" operates in poor neighborhoods, exchanging sorted trash for rice, vegetables or other farm produce collected from the area's surplus production. In these and other ways, Curitiba has lessons not only for developing countries, but cities everywhere.
The United Nations agency, Habitat, has set up programs to help the urban poor in the developing world. An assumption it shares with both the World Bank and the International Monetary Fund is that urbanization is inevitable -- though for it and many urban ecologists, it is as important to address the root causes of rural decline as to work to change big cities.
"This issue is very relevant," says Jennifer McGuinn of the Hungary-based nonprofit Regional Environmental Center of Central and Eastern Europe. "Accession to the European Union in 2004 will come as a shock to many farmers in Eastern Europe, who won't be able to compete with existing EU farmers. We must develop local economic initiatives to prevent migration."
One of the urban ecology movement's early conferences, "EcoCity," held in 1996 in the traditional fishing village of Yoff, Senegal, reminded participants how practices such as organic farming, rainwater harvesting, composting, community and local democracy are ancient traditions still flourishing in towns and villages across Africa. The meeting of activists, researchers and representatives of NGOs and other agencies, showed African participants in particular that these were traditions worth holding on to. As cities worldwide continue to grow and spread out of control, urban ecology may be a movement whose time has come -- again.