Deadly Heat Exposure in an Urbanized World

Climate-change exposes an increasing share of the world population to potentially lethal heat, a threat accentuated by rapid urbanization. Here, we project occurrence of future deadly heat for urban agglomerations around the world until 2080 by using CMIP6 climate model projections of temperature and relative humidity, urbanization prospects and GDP projections from the SSP scenarios. We show that while nearly all regions within latitudes 35°S - 45°N experience an increase in days of deadly heat, Sub-Saharan Africa and Southeastern Asia are particularly exposed, a trend exacerbated by rapid urbanization. By 2080, between 2.3 (59\%) (SSP1-2.6) and 3.0 (75\%) (SSP5-8.5) billion urban dwellers will experience more than 30 annual days of deadly heat, including 477 (66\%) - 546 (77\%) million in Sub-Saharan Africa and 988 (93\%) - 993 million (94\%) in South and South-Eastern Asia. The exposure to heat is highly unequal, with some of the poorest regions affected the most. Our results imply that jointly mitigating climate change, planning for well-ventilated cities, and combating poverty to enable economic access to air conditioning is required to avert a global-scale humanitarian crisis.