How has climate change affected cities?

January 1, 2012

How has climate change affected cities?

The first snow fell early this autumn in the northeastern United States. Yet the somewhat premature winter weather may be deceiving. According to the U.S. Environmental Protection Agency, human behavior has contributed to global climate change, and we are likely to face steadily rising temperatures in the future. These record-high temperatures are significantly affecting the health of at-risk populations such as the elderly. For example, the 2011 heat wave that enveloped the midwestern and eastern regions of the United States claimed a dozen lives in the Midwest.

In their summary of epidemiological studies between 2005 and 2010, sociologist Sharon Harlan and geographer Darren Ruddell argued that the effects of higher temperatures will hit cities harder than rural areas. Their review showed that cities’ population density and towering buildings create a phenomenon known as the “urban island effect.” The densely built urban landscape retains heat more easily and creates higher baseline temperatures than those found in less populated small towns or villages. Yet researchers are still questioning how exactly climate change affects urban populations.

Rising temperatures and heat-related mortality

In a recent study, geographers Simon Gosling and Glenn McGregor and epidemiologist Anna Páldy investigated the relationship between rising temperatures and mortality in six cities. Relying on death records for residents of Boston, Budapest, Dallas, Lisbon, London, and Sydney, they argued that there is a relationship between excess mortality—mortality that would exceed the usual average at a particular time of the year—and rising temperatures. In cooler-weather cities, where residents are accustomed to lower baseline temperatures, heat-related mortality occurs at lower temperatures than it does in cities that have warmer climates. In a follow-up study, Gosling, McGregor, and climatologist Jason Lowe attempted to project the death toll that rising temperatures may help create in the future. Such calculations, they found, are almost impossible to determine, since the models cannot account for the adaptation of the population to higher temperatures. For example, projecting that people would be able to adjust effectively to an average temperature increase of just two degrees Celsius would cut the heat-related mortality rate in half.

Uncertainty about our ability to project mortality rates accurately is offset by the reality of the heat waves that have significantly affected residents of several large cities numerous times over the last decade. Marc Poumadère, Claire Mays, Sophie Le Mer, and Russell Blong showed that the 2003 heat wave in France caused 14,947 excess deaths. Those who fell victim to the high temperatures were often isolated, economically disadvantaged, or living in small and poorly ventilated apartments. A similar assessment was made by sociologist Eric Klinenberg, who argued that the 1995 heat wave in Chicago disproportionately affected older African Americans. Not only were many elderly African American seniors living in poorly ventilated apartments, but many were living in neighborhoods rife with violence, which prevented them from leaving their homes to seek help.

Possible solutions

While some characteristics of cities, such as their density and their tall buildings, might contribute to and magnify the effects of climate change, some researchers argue that those very attributes might be part of the solution. Economists Edward Glaeser and Matthew Kahn analyzed the National Household Travel Survey and found that the density of cities and their ability to support carbon dioxide emission–reducing solutions such as mass transit made urban areas particularly efficient at addressing one of the leading causes of global warming. In cities with well-developed public transit systems, such as Boston and New York, residents can drastically reduce their use of cars. Densely populated cities with extensive public transportation systems thus have far lower carbon dioxide emission rates than suburban areas. Many cities in the Northeast and on the West Coast of the United States, such as New York and San Francisco, are also on the forefront of reducing electricity use.

Encouraging people to live in cities, even despite the higher baseline temperatures, might be a solution to lowering carbon dioxide emissions. As Stephen Hammer, co-director of the Urban Climate Change Research Network, recently pointed out in a CNN interview, cities are actually using energy very efficiently—it is simply the sheer number of people living in cities that leads to comparatively high emission rates. He calls cities the “laboratory for central governments.” According to Hammer, urban areas’ innovative approaches to protecting the environment can lead the way to national implementation of policies that could promote more sustainable practices. With their ability to innovate and adapt, cities could be a model for a more environmentally friendly lifestyle that may prevent or delay further climate change and its effects.

Homepage image by Flickr user jo3design.