The confluence of heat and air pollution disproportionately increases the risk of death, a new study published in the American Journal of Respiratory and Critical Care Medicine finds. Extreme heat and heatwaves are made worse and more frequent by climate change, mainly caused by the combustion of fossil fuels — which also produces huge amounts of particulate matter pollution. Reviewing more than 1.5 million deaths in California between 2014 and 2019, researchers found a 6% risk of death increase on hot days, a 5% risk of death increase on days with high PM2.5 pollution, and a 21% risk of death increase on days with both.

Racist policy decisions, both historically and today, subject people of color to disproportionate heat and pollution burdens, with the elderly, unhoused people, and those who work outside being most exposed. Extreme heat also exacerbates wildfires which release enormous amounts of particulate matter. The study’s publication comes as large swaths of the Northern Hemisphere stifle under extreme heat and increased wildfire threats. (Study: E&E $; European heat and wildfires: Reuters, AP, Axios, Washington Post $, AP, Reuters, CBS; Climate Signals background: Extreme heat and heatwaves; Wildfires)