Local Drivers in Accelerating North American Heat Stress

Climate change increases the frequency and intensity of heat extremes, threatening human health and economies1–4. We use reanalysis data and regional climate simulations with a 4- km grid5 to calculate the wet-bulb globe temperature (WBGT)6, a key index for assessing heat stress7, 8. Our analysis shows that historical climate change has increased population exposure to extreme heat (WBGT >32,◦ 17 C) by 21% across the Contiguous United States. However, as global warming reaches 2,◦C, exposure surges by 273% due to the exponential rise in heat stress frequency with temperature. Annual maximum WBGT increases fastest in high-latitude areas, while BFH frequency increases most in humid subtropical regions like 1the Gulf Coast and the Caribbean. In northern regions, heatwave frequency increases with warming while in southern regions individual events merge into mega-heatwaves lasting over a month under 2 ◦C warming. Drivers of WBGT changes differ by region, with temperature and longwave radiation dominating maintain and high-latitude land areas. Humidity plays a crucial role in humid subtropical regions, while decreasing wind speeds impact the Midwest and Northeast. These regional differences highlight the need for tailored adaptation strate gies. Our findings stress the urgent need for mitigation and adaptation strategies to protect vulnerable populations from rising heat-related risks9–12.