Impact of climate and population changes on the increasing exposure to summertime compound hot extremes

Attributing the changes in the population exposure to global compound hot extremes, which combine daytime-nighttime hot extremes with more severe impacts, is essential for climate change adaptation. Based on daily temperature data from the Coupled Model Intercomparison Project phase 6 (CMIP6) and population data, we estimate the changes in population exposure for two future periods under three scenarios of emission and socio-economic development at global and continental scales, and assess the contributions from climate and population changes. We find that the spatial patterns of exposure to compound hot extremes are similar for different periods and scenarios, and regions with high exposure are mainly located over East Asia, South Asia, Europe, and parts of eastern USA and Africa. The exposure shows an increase from baseline (1980-2014) to mid- and late 21st century periods (2021-2055 and 2056-2090) in most regions worldwide. Under the business-as-usual scenario (SSP2-4.5), the global exposure increases by similar to 19-fold during the late 21st century, and Africa shows the largest increase while Europe shows the smallest. Early (SSP1-2.6) and no (SSP5-8.5) actions of mitigation would relieve and aggravate the increase rate, respectively. For about 78%-87% of the global land areas, the changes in exposure are mainly caused by climate change (accounting for >69%), followed by the interaction effect (accounting for similar to 29%) that refers to synergistic changes in climate and population. In parts of mid- to high-latitude regions, the exposure is smaller than expected due to opposite effects of climate change and population change. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study finds that the spatial patterns of exposure to compound hot extremes are similar for different periods and scenarios, with regions in East Asia, South Asia, Europe, parts of the eastern USA and Africa showing high exposure. Under a business-as-usual scenario, global exposure increases significantly by the late 21st century, with early and no actions of mitigation relieving and aggravating the increase rate respectively. Climate change is the main driver of global exposure changes, with some regions experiencing smaller exposure than expected due to opposite effects of climate and population changes.