Cities across the globe are gasping in extreme summer heat. Last week, the United Kingdom—known for its cool, rainy climate—broke its all-time-high temperature record, topping out at 104.4 degrees Fahrenheit. Meanwhile, U.S. cities are scrambling to protect their residents and physical infrastructure from the dangers of extreme heat, which can cause school closures, transit system malfunctions, strained electrical grids, and more. Extreme heat kills over 600 people in the U.S. each year; older adults, very young children, and people with chronic diseases are the most vulnerable. 

Climate change is worsening these trends. By the end of the century, realistic scenarios project that the planet will get 5 to 6 degrees warmer. Urban areas are particularly affected, as large residential and commercial buildings, roads, sidewalks, and other impervious surfaces throughout the built environment create heat islands that absorb and retain heat during the hottest times of the day and reduce cooling overnight. Under these projections, when faced with a once-in-a-generation heat wave, more than 20,000 lives could be lost in major U.S. cities. 

Through indoor air conditioning, the U.S. is much better equipped to keep people safe during periods of extreme heat compared with a century ago. Nationally, about 70% of homes now have central AC, while about 10% of households have no air conditioning. But the presence and type of home AC varies considerably by geography. Like exposure to other climate risks, protection from extreme heat also varies by income, tenure, and race. 

Access to home AC varies across the US, largely—but not entirely—reflecting regional differences in climate. In Southeast and Southwest metro areas such as Atlanta, Houston, and Phoenix, 95% of homes are at least partially cooled by central air, while less than 3% have no air conditioning. (The Census Bureau’s American Housing Survey asks households whether any part of the house has AC.) West Coast metro areas such as Seattle, San Francisco, and San Jose, Calif. have the highest share of homes with no AC, while Northeast and Midwest metro areas with older housing stock tend to have more homes that rely on window AC units. 

Read the full article about air conditioning access by Rebecca Mann and Jenny Schuetz at Brookings.