Impact of population aging on future temperature-related mortality at different global warming levels

Abstract

Older adults are generally amongst the most vulnerable to heat and cold. While temperature-related health impacts are projected to increase with global warming, the influence of population aging on these trends remains unclear. Here we show that at 1.5 °C, 2 °C, and 3 °C of global warming, heat-related mortality in 800 locations across 50 countries/areas will increase by 0.5%, 1.0%, and 2.5%, respectively; among which 1 in 5 to 1 in 4 heat-related deaths can be attributed to population aging. Despite a projected decrease in cold-related mortality due to progressive warming alone, population aging will mostly counteract this trend, leading to a net increase in cold-related mortality by 0.1%-0.4% at 1.5-3 °C global warming. Our findings indicate that population aging constitutes a crucial driver for future heat- and cold-related deaths, with increasing mortality burden for both heat and cold due to the aging population.

Fig. 1. Projections of average daily mean temperature changes under global warming levels.

Distribution of the 800 locations with projected temperature changes at 1.5 °C, 2 °C, and 3 °C) of global warming. The future periods in which the 20-year running mean of global mean temperature first reaches the 1.5 °C, 2 °C, and 3 °C of warming above pre-industrial level (1850–1900) are 2018–2037, 2032–2051, and 2055–2074, respectively under SSP5-8.5. The administrative map data is from the giscoR package (https://ropengov.github.io/giscoR/).

Fig. 2. Population aging at 20-year periods corresponding to different levels (1.5 °C, 2 °C, and 3 °C - SSP5-8.5) of global warming by country/area.

Country/area-specific age-group population projections are derived from the SSP5 scenario in the first 20-year periods reaching 1.5 °C (2018–2037), 2 °C (2032–2051), and 3 °C (2055–2074) of warming, respectively. X-axis shows the changes in percentage of population ≥ 65 years (%).

Fig. 3. Changes in cold-related excess mortality fractions (%) at different levels of global warming by country/area under the climate-population and climate-only scenarios, compared with the historical period (1995–2014).

Estimates (shown as dots) are reported as the ensemble average of 18 general circulation models under the SSP5-8.5 scenario. The whiskers represent the 95% empirical confidence intervals. The future periods in which the 20-year running mean of global mean temperature first reaches the 1.5 °C, 2 °C, and 3 °C of warming above pre-industrial level (1850–1900) are 2018–2037, 2032–2051, and 2055–2074, respectively under SSP5-8.5.

Fig. 4. Changes in heat-related excess mortality fractions (%) at different levels of global warming by country/area under the climate-population and climate-only scenarios, compared with the historical period (1995–2014).

Estimates (shown as dots) are reported as the ensemble average of 18 general circulation models under the SSP5-8.5 scenario. The whiskers represent the 95% empirical confidence intervals. The future periods in which the 20-year running mean of global mean temperature first reaches the 1.5 °C, 2 °C, and 3 °C of warming above pre-industrial level (1850–1900) are 2018–2037, 2032–2051, and 2055–2074, respectively under SSP5-8.5.

Fig. 5. Contributions of climate change and population change to the changes in cold- and heat-related mortality at different levels of global warming.

A change in cold-related excess mortality fraction (%); B change in heat-related excess mortality fraction (%). Country/area-level changes by climate change and population aging are shown at 1.5 °C, 2 °C, and 3 °C of global warming using a 20-year window compared with the historical period 1995–2014 under SSP5-8.5. The future periods in which the 20-year running mean of global mean temperature first reaches the 1.5 °C, 2 °C, and 3 °C of warming above pre-industrial level (1850–1900) are 2018–2037, 2032–2051, and 2055–2074, respectively under SSP5-8.5. The impact of population aging was estimated by subtracting the future changes in temperature-related impacts in the constant population scenario (“climate-only”) from the changes in temperature-related impacts under the SSP5 mortality projection in the “climate-population” scenario. Note the different scales in the x-axis used for heat and cold.

Fig. 6. Contributions of climate change and population change to the changes in non-optimal temperature-related (heat and cold combined) mortality at different levels of global warming.

Country/area-level changes by climate change and population aging are shown at 1.5 °C, 2 °C, and 3 °C of global warming using 20-year window compared with the historical period 1995-2014 under SSP5-8.5. The future periods in which the 20-year running mean of global mean temperature first reaches the 1.5 °C, 2 °C, and 3 °C of warming above pre-industrial level (1850–1900) are 2018–2037, 2032–2051, and 2055–2074, respectively under SSP5-8.5. The impact of population aging was estimated by subtracting the future changes in temperature-related impacts in the constant population scenario (climate-only) from the changes in temperature-related impacts under SSP5 mortality projection in the climate-population scenario.