Nationwide projections of heat- and cold-related mortality impacts under various climate change and population development scenarios in Switzerland

Abstract

Climate change and progressive population development (i.e., ageing and changes in population size) are altering the temporal patterns of temperature-related mortality in Switzerland. However, limited evidence exists on how current trends in heat- and cold-related mortality would evolve in future decades under composite scenarios of global warming and population development. Moreover, the contribution of these drivers to future mortality impacts is not well-understood. Therefore, we aimed to project heat- and cold-related mortality in Switzerland under various combinations of emission and population development scenarios and to disentangle the contribution of each of these two drivers using high-resolution mortality and temperature data. We combined age-specific (<75 and ⩾75 years) temperature-mortality associations in each district in Switzerland (1990-2010), estimated through a two-stage time series analysis, with 2 km downscaled CMIP5 temperature data and population and mortality rate projections under two scenarios: RCP4.5/SSP2 and RCP8.5/SSP5. We derived heat and cold-related mortality for different warming targets (1.5 °C, 2.0 °C and 3.0 °C) using different emission and population development scenarios and compared this to the baseline period (1990-2010). Heat-related mortality is projected to increase from 312 (116; 510) in the 1990-2010 period to 1274 (537; 2284) annual deaths under 2.0 °C of warming (RCP4.5/SSP2) and to 1871 (791; 3284) under 3.0 °C of warming (RCP8.5/SSP5). Cold-related mortality will substantially increase from 4069 (1898; 6016) to 6558 (3223; 9589) annual deaths under 2.0 °C (RCP4.5/SSP2) and to 5997 (2951; 8759) under 3.0 °C (RCP8.5/SSP5). Moreover, while the increase in cold-related mortality is solely driven by population development, for heat, both components (i.e., changes in climate and population) have a similar contribution of around 50% to the projected heat-related mortality trends. In conclusion, our findings suggest that both heat- and cold-related mortality will substantially increase under all scenarios of climate change and population development in Switzerland. Population development will lead to an increase in cold-related mortality despite the decrease in cold temperature under warmer scenarios. Whereas the combination of the progressive warming of the climate and population development will substantially increase and exacerbate the total temperature-related mortality burden in Switzerland.

Keywords: distributed lag non-linear model; heat and cold; mortality; nationwide analysis; representative concentration pathways; shared socioeconomic pathways.

Figure 1

Projected annual mean temperature and age-specific mortality trends by Representative Concentration Pathways (RCP) and Shared-Socioeconomic Pathway scenarios (SSP) and the periods defined for each warming target in Switzerland. The observed temperature for the baseline period is indicated in grey, and the projected annual temperature for RCP4.5/SSP2 is in blue and in red for RCP8.5/SSP5. Age-specific projected annual deaths are represented for under 75 years (green), over and equal 75 years (purple) and total projected annual deaths (pink). The 21 year warming targets are represented with the colored panels (yellow 1.5 °C, orange 2 °C, red 3 °C) and the baseline period in grey.

Figure 2

Pooled temperature-mortality association by age group (1990–2010). The pooled temperature mortality association was derived from the meta-analytical model (stage two) for below 75 years, and 75 years and older between 1990 and 2010 in Switzerland, with the vertical line in blue representing the 1st percentile (extreme cold) and in red the 99th percentile (extreme heat).

Figure 3

Projected heat- (A) and cold-related (B) excess mortality rates per 100 000 people by warming target for each district in Switzerland for RCP4.5/SSP2 and RCP8.5/SSP5.

Figure 4

Projected annual heat- and cold-related deaths by RCP/SSP scenario and warming target in Switzerland and for the baseline period (1990–2010), and the corresponding difference in burden from the baseline period (1990–2010). The projected cold-related deaths are represented in blue and in red for heat, with the corresponding 95%CI by warming target. The black line indicates the absolute difference in cold- and heat-related mortality by warming compared to the baseline scenario with the corresponding 95%CI.

Figure 5

Projected annual heat- and cold-related deaths by RCP/SSP scenario and warming target in Switzerland relative to the baseline (1990–2010), with the contribution of individuals drivers (population development and climate contribution). The contribution of population development is indicated in green, while the contribution of temperature is indicated in yellow. Overall projected heat- and cold-related mortality is indicated in red and blue, respectively.