Study Says Rethinking Cities Is Key to Climate Change

Cities generate most of the world's greenhouse gas (GHG) emissions. So changing their configuration and altering the lifestyles of urban dwellers can have a major impact on mitigating those emissions and reducing their contribution to global warming, according to a new study led by analysts at the World Bank in Washington, D.C.

Today's urban residents make up half of the world's population but account for 71% of energy-related greenhouse gas emissions. That fraction is expected to rise to 76% by 2030. To better understand today's sources of greenhouse gases, Daniel Hoornweg and his colleagues compiled a GHG emissions inventory for 100 cities in countries around the world.

They found that annual per capita emissions range from the equivalent of 30 metric tons to 0.5 metric tons of carbon dioxide. The disparity is due not just to consumption patterns but also to the urban environment itself, they note in an article released online this month in Environment and Urbanization. Residents of New York City generate half the per capita emissions of greenhouse gas emissions as their urban counterparts in Denver, for example, while per capita emissions for residents of downtown Toronto, Canada, are one-tenth that of their suburban neighbors. "The vast majority of emissions are associated with the lifestyles of the rich, including where they choose to live," says Hoornweg.

The authors suggest that urban planners in fast-growing cities in China and elsewhere could best mitigate emissions by building infrastructure and housing that result in densely populated yet livable city centers. On a broader scale, cities and regions could cooperate by insisting upon greener sources of electrical power. "There's a lot of fundamental change that could result from redesigning cities and their infrastructure," says Christopher Kennedy, a civil engineer at the University of Toronto.