Climate Change and Disparities in Extreme Heat Exposure for Socially Vulnerable Areas in the Contiguous United States

Climate change disproportionately impacts vulnerable communities around the globe. Previous work has shown that more socially vulnerable communities at the city and regional level within the contiguous United States (CONUS) are exposed to higher temperatures, but high-resolution downscaled climate model data employed in the 5th US National Climate Assessment has not been used to assess future temperature exposure disparities under Global Warming Levels (GWLs). We assess past and future average daily maximum temperature exposure across the CONUS in high- and low-vulnerability locations using a social vulnerability index (SVI). We find that the disparity in temperature exposure for high-SVI areas increased from ~1.3°C (1951-1980) to ~1.6°C (1994-2023). Using an ensemble of downscaled climate models, we assess future impacts at GWLs of 1.5°C, 2°C, and 3°C. Specifically, we compare the number of days/year that exceed air temperature thresholds recommended for safe fan use (35°C, 39°C) in high-SVI and low-SVI areas. We find that for exposure to a 35°C air temperature threshold, at 1.5°C global warming there is an average annual exposure difference of ~16 days, at 2°C ~18 days, and at 3°C ~22 days. For exposure to a 39°C threshold, at 1.5°C global warming there is an
exposure difference of ~5 days, at 2°C ~6 days, and at 3°C ~9 days. These results highlight that in many high-SVI areas future warming will disproportionately increase the number of days exceeding adaptation-relevant temperature thresholds. These findings further support the need to slow global warming and direct adaptation efforts towards more vulnerable communities.