In 1995, a heatwave in Chicago in July killed more than 700 people in five days—the most devastating climate disaster in Illinois history. State authorities explained that the high fatality rate was due to an inadequate local heat warning system, lack of ambulance services, and an aging population in urban areas. Analysis by Eric Klinenberg, author of Heat Wave: A Social Autopsy of Disaster in Chicago, however, points to causes more closely related to social equity. Klinenberg’s map of heat-related deaths in Chicago matches the distribution of poverty and urban abandonment. The 2018 documentary film, Cooked: Survival by Zip Code highlights a surprisingly close correlation between heat wave deaths and areas that are food deserts and have a high incidence of gun-related crimes, diabetes, breast cancer, unemployment, and heart disease, and low high school completion rates.
Chicago’s social disaster of 25 years ago is still repeating itself today. According to a recent study published in the journal Nature Communications, heat stress—a significant risk to public health—is unequally distributed across income groups in major U.S. cities. More people of color live in places with little green space and lots of driveways, buildings, and blacktop.
Due to the urban heat islands effect, cities with more than a million people are about 1.8-5.4°F (1-3°C) warmer than average and in the evening, cities can be 22°F(12°C) warmer than the surrounding areas. Humid regions and cities with denser populations experience the most significant temperature differences. Urban heat islands form as a result of several factors: 1) Hard, dry surfaces like sidewalks and roofs in urban areas provide less shade and moisture than natural landscapes; 2) heat is generated from human activities such as vehicles, A/C, and industrial facilities; and 3) the spacing of buildings influences wind flow and release solar energy. The urban heat island effect is not just about temperature but more about human health, well-being and quality of life. Dense residential areas and industrial zones paved with asphalt absorb and radiate solar energy while large parks and green spaces cool down the surrounding areas.
Figure 1. Baltimore Heating Map
According to the joint research by NPR and University of Maryland’s Howard Center, three-quarters of the 97 most populous U.S. cities show that areas with higher temperatures were more impoverished. In other words, low-income households in large cities are more exposed to heatwaves than wealthier households as global warming accelerates. The heat mapping project at Portland State University also shows that the temperature can vary as much as 20°F across different parts of the same city. For example, in Baltimore, rowhouse areas where many low-income families live are hotter, and the residential regions around parks are relatively cool, resulting in a temperature difference of more than 10°F (see Figure 1).
Measures to reduce climate injustices associated with urban heat islands are a growing area of urban policy and planning. Baltimore’ ‘B’more Cool’ project, launched in 2014, works to improve our understanding of urban heat islands and identify ways to reduce their impacts. With the collaboration of scientists, urban designers, city officials and local community groups, Baltimore has installed cool roofs, replaced vacant lot spaces with community green spaces, and opened more cooling centers to improve community resilience. Washington D.C. has a goal to cover 40 percent of the city with the tree canopy and the Portland city council has proposed new requirements to limit the amount of pavement and asphalt-covered area. Although programs like these will take some time to reduce urban heat island impacts, their existence is a positive step towards addressing critical social equity concerns.
