Projections of Heat- and Cold-Related Mortality Under Climate Change Scenarios in Portugal: A Modelling Study

Climate change and related events such as temperature increase over time and more frequent extreme weather events constitute a risk to the population and wellbeing. This study contributes to the knowledge on this subject by analyzing changes in mortality in Portugal using the most recent historical and future climate projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6). A time-series distributed lag non-linear model (DLNM) was used to estimate the temperature-related mortality burdens in Portugal in the historical period (or reference, 1995&ndash:2014), the mid-century period (2046&ndash:2065), and the end of the century period (2081&ndash:2100) under moderate (SSP2-4.5) and extreme (SSP5-8.5) climate change scenarios. The findings show that winter periods of the contemporary climate (1995&ndash:2014) showed a significantly elevated risk of deaths from cold temperatures (RR = 2.23 (95% CI: 1.07, 4.64) at a minimum value of &minus:3 &deg:C), while at the maximum value (35.9 &deg:C), the RR of 1.69 (95% CI: 1.01, 2.82) in the summer period indicated a moderate increase in risk. In terms of future projections, heat-related and extreme-heat-related mortality are higher under SSP5-8.5, while cold-related and extreme-cold-related mortality are generally higher under SSP2-4.5. Under the SSP2-4.5 scenario, the future periods of 2046&ndash:2065 and 2081&ndash:2100 showed a small net change in heat-related mortality. However, there is projected to be an increase in heat-related mortality due to increased heat, ranging from 0.13% to 0.14%. The impact of extreme heat is expected to result in a mortality increase of 0.03% to 0.04%, while extreme cold is expected to decrease mortality by &minus:0.10%. Under the SSP5-8.5 scenario, the net change in mortality during the future period of 2046&ndash:2065 is estimated to decrease by &minus:0.13%, with some uncertainty in the estimate. From 2081 to 2100, there is expected to be an estimated increase of 0.06% in mortality. The specific impact of increased heat shows an increase in heat-related mortality ranging from 0.15% to 0.17%, while extreme heat has an estimated increase of 0.04% to 0.05%. The developed framework provides a comprehensive assessment of excess mortality attributed to varying non-optimum temperatures for designing public health policies in Portugal.