FORUM Green Urban Worlds Jennifer Wolch Department of Geography, University of Southern California Contemporary cities are unsustainable, compromising the health and well-being of coming generations. How can geographers help imagine and build cities that hold more promise for the future? I suggest that the answer lies in addressing three fundamental challenges facing society today: restoring the city’s ecological integrity, redesigning systems of production and consumption, and recasting urban citizenship to promote social and ecological justice. Using the example of the Los Angeles River, I explore how multidisciplinary urban geographic research can help us think about these challenges, and contribute to the development of greener, more sustainable cities. Key Words: industrial ecology, Los Angeles River, socio-ecological planning, sustainable citizenship, sustainability. G eographers are well aware that the earth’s population is rapidly, if unevenly, urbanizing, making ours a decidedly urban world. Much of this urban world is grey, paved with concrete and as- phalt, and/or brown, polluted by industry, automobiles, and waste. The challenges of the urban present give rise to widespread trepidation and distrust in our ability to leave a legacy of healthy communities to future gener- ations. Even in the richest cities in the richest nations, residents live in a frightening riskscape of toxic soils, airborne pollutants, sullied water supplies, and vanishing species. In this article, I confront our fears and offer some glimpses of what alternative ‘‘green’’ urban worlds might look like. By doing so, I seek to inspire hope for a healthier planet and belief in the possibility of a more sustainable future, and to motivate the activism neces- sary to change course. I also show how as geographers we are particularly well positioned to help greener urban worlds emerge. Twentieth-century ideas about cities were rooted in a deeply ingrained dualism between city and wilderness, nature and culture. Urban geographers shared this out- look. For example, Chicago School human ecologists predicated their theories of the city on ecological met- aphors but they were not concerned with nonhuman natures per se: they counted hobos and juvenile delin- quents and women who voted but they did not count prairie grasses or hedgehogs. Later versions of urban geography were very different, but their objects of analysis were thoroughly humanized cities and suburbs from which nature was excluded. Exactly how cities got built and used, and their impacts, depended on who was talking. For urbanists grounded in neoclassical theory, cities were built by rational producers and consumers, had orderly, quantifiable bid-rent curves, predictable land use patterns, and residential and commute patterns guided by the invisible hand and competitive local governments in service to the median voter (Tiebout 1956; Alonso 1964; Berry and Horton 1970). For those of a more materialist orientation, cities arose through the habits of capital, class struggles, racial formations, and gender divisions, regulated by urban growth machines and their shadow state apparatchiks (Harvey 1973; Dear and Scott 1981; McDowell 1983; Logan and Molotch 1987; Wolch 1990; Pratt and Hanson 1995). But re- gardless of stripe, most twentieth-century urban geog- raphers did not think about urban rivers or oak trees or red-legged frogs. Things are changing. Late-twentieth-century science and activism highlighted the severity of pollution prob- lems, resource depletion, and habitat destruction. Granted the complex links between population and re- sources, awareness of carrying capacity hinted that new, less wasteful settlement patterns—with smaller eco- logical footprints—might be vital in an urbanizing world (Wackernagel and Rees 1996). International summits, commissions, and reports, notably the Bruntland Com- mission’s Our Common Future (WCED 1987), brought out, both in what was and was not said, the conflicts between North and South and between environmental protection and economic development, and introduced heated debates about sustainable development, eco- logical modernization, and ecological sustainability (Redclift 1987; Sachs 1993; Dobson 1996; McManus Annals of the Association of American Geographers, 97(2), 2007, pp. 373–384 r 2007 by Association of American Geographers Initial submission, August 2005; revised submission, May 2006; final acceptance, December 2006 Published by Blackwell Publishing, 350 Main Street, Malden, MA 02148, and 9600 Garsington Road, Oxford OX4 2DQ, U.K.