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Social equity and global impacts are missing from measures of cities' environmental friendliness, write David Wachsmuth, Daniel Aldana Cohen and Hillary Angelo.
Manhattan skyscrapers, rather than rustic rural towns, are quickly becoming the picture of sustainable living in the twenty-first century. San Francisco, Copenhagen and Singapore each top their regions in the Green City Index (see go.nature.com/2bxjac9). As sites of innovation and economic dynamism, these places exemplify a blend of density and livability that large, prosperous cities in the 'global south', such as Mumbai in India and São Paulo in Brazil, increasingly emulate.
A few decades ago, cities were seen as sustainability problems rather than solutions. Then, as concerns about suburban sprawl, shanty towns and climate change grew, so too did awareness that clustering people in energy-efficient buildings and walkable, shady neighbourhoods makes cities more pleasant to live in and better for the global environment.
But the prevailing model of urban sustainability is too narrow. Although the social, economic and ecological issues behind sustainability problems are regional or global in scale, urban policy usually addresses single ecological issues in individual neighbourhoods. Focusing on dense cities and their affluent areas ignores social movements and their advocacy for quality-of-life issues such as housing and commuting, which have direct ecological consequences. Targeting specific districts ignores the often negative regional and global impacts of local environmental, or 'greening', improvements.
Spatially, sustainability research and policymaking should shift focus from city centres to urban regions and global networks of production, consumption and distribution. Socially, policymakers should incorporate equity into every stage of the urban-policy process, from research to formulation to implementation.
NEIGHBOURHOOD WATCH
From the revitalization of city parks to urban bicycle-sharing programmes, urban sustainability interventions tend to be conceived, implemented and evaluated one municipality or neighbourhood at a time. Yet urban environmental processes occur on much larger scales. Projects that benefit one district may have negative impacts next door.
One example is environmental gentrification. As districts become greener, they become more desirable and expensive. The premiums placed on neighbourhood amenities - such as walkability, public transport and the proximity of parks, farmers' markets and 'greenways' such as hiking trails and bike paths - by residents who can afford to pursue them raise the cost of living.
Social displacement can...