Projecting Global Mortality Due to Non-Optimal Temperature From 2020 to 2100: A Global Burden of Disease Forecasting Study

Abstract

Background: The Global Burden of Disease Study 2019 (GBD 2019) estimated that approximately 2 million (95% uncertainty interval [UI] 1·7–2·3) deaths and 37·8 million (32·2–47·6) DALYs were attributable to non-optimal temperature in 2019. Globally, most of this burden was attributed to low temperatures, but high heat-attributable mortality rates were observed in warmer regions such as south Asia, north Africa and the Middle East, and sub-Saharan Africa. The impact of increases in global temperatures and demographic trends on future temperature-related mortality is unclear. Methods: We linked cause-specific temperature-mortality risk curves to daily temperature forecasts from the NEX-GDDP dataset. The NEX-GDDP data set comprises 21 individual General Circulation Models (GCM) that were spatially downscaled for two Representative Concentration Pathways (RCPs): RCP4.5 and RCP8.5. For each pixel, day, and cause, we estimated the population attributable fraction (PAF) based on the risk of cause-specific mortality at a given temperature relative to the theoretical minimum risk exposure level (TMREL); we then estimated temperature-attributable deaths by multiplying these PAFs with location-specific mortality estimates for the reference period from 1990 to 2020 and for the forecasted period from 2020 to 2100. Other upstream drivers in the model, including the Socio-demographic Index and air pollution levels, were held constant. Findings: Globally, we estimate increases in the number and rate of deaths attributable to non-optimal temperature, with 3.27 (2.11 – 4.70) million and 4.08 (2.67 – 5.86) million annual deaths by the end of the century, for RCP4.5 and RCP8.5, respectively. These increases are driven largely by heat-attributable burden, with smaller and more variable changes in cold-attributable deaths. Warm, low-latitude regions will be disproportionally affected, with the largest increases in temperature-attributable mortality expected in sub-Saharan Africa, south Asia, and Latin America and the Caribbean. As our study accounts for adaptation and does not extrapolate relative risks beyond the exposure currently experienced, these estimates are likely conservative. Interpretation: Globally increasing temperatures are projected to substantially increase the mortality burden attributable to non-optimal temperature. Higher global temperatures only lead to minor decreases in cold-related mortality which do not offset increases in heat-related mortality. Funding Statement: Bill & Melinda Gates Foundation Declaration of Interests: None to declare.