Attributing observed trends in heat-related excess mortality to climate change

Past studies quantifying the burden of heat-related mortality attributable to climate change have mostly focused on specific extreme events or considered multi-decadal averages. Here, we contribute to the scarce literature on the attribution of observed temporal trends in heat-related mortality to climate change. Our study is based on daily all-cause mortality time-series from 15 major German cities over 1993-2020. Counterfactual climate data is derived from century-long measurement series of daily mean temperatures by removing trends related to the observed rise in global mean temperature according to the ATTRICI method. We use quasi-Poisson regression models including distributed lag non-linear models and multivariate meta-regression models to estimate temperature mortality associations. Our results corroborate previous model-based estimates, suggesting that, averaged over the entire study period, 28% (95%CI: 17%, 42%) of warm-season (May-Sep) heat-related excess mortality across all German cities were attributable to climate change. Considering linear temporal trends suggests that this proportion has increased by 4.0±1.0% per decade. Under observed climate change, we find a linear increase of 174 (SE: ±151) heat-associated deaths per decade across cities. By contrast, our results suggest that without climate change there would not have been a significant increase in heat associated deaths. Overall, our study provides evidence of increasing impacts of climate change on heat-related mortality in Germany since the 1990s. As temperatures keep rising in the future, climate change is expected to drive further increases in heat-related excess mortality unless additional adaptive measures are taken.