Increasingly frequent power failures combined with heatwaves fueled by climate change pose severe, compounding threats to major American cities, new research suggests. The study, published in Environmental Science & Technology, looked at Atlanta, Detroit, and Phoenix and found at least two-thirds of residents in those cities would be vulnerable to heat exhaustion or heat stroke in the event of an overlapping heatwave and blackout.

“A widespread blackout during an intense heat wave may be the deadliest climate-related event we can imagine,” Brian Stone Jr., a professor at the School of City & Regional Planning at Georgia Institute of Technology and the lead author of the study, told the New York Times. Extreme heat, made worse by climate change caused by extracting and burning fossil fuels, is already the deadliest type of severe-weather event, killing as many as 12,000 people in the U.S. every year.

The human health harms caused by extreme heat heighten societal inequities — extreme heat danger is often worst in historically redlined neighborhoods. The legacy of racist redlining policies, including the dearth of greenspace that worsens heat islands, exacerbates extreme heat in neighborhoods predominantly populated by people of color. Heatwaves also put greater demand on the electrical grid as air conditioners are forced to work harder. The number of blackouts in the U.S. doubled between 2015 and 2020, and Stone said “the probability of a concurrent heat wave and blackout event is very likely rising as well.” (New York Times $)