Attributing heatwave mortality to human-induced climate change in Greece: a case-crossover and attribution analysis for 2000-2019

Background Heatwaves increasingly threaten public health in the Mediterranean region, and Greece is among the hardest hit countries. Yet evidence on long-term adaptation, spatial vulnerability, and the contribution of human-induced climate change to heatwave-related mortality in Greece remains limited. Methods We analysed 2,144,957 all cause deaths in Greece during 2000 and 2019 using a time stratified case crossover design. We derived population weighted daily maximum temperatures at NUTS3 level from ERA5 reanalysis and WorldPop. We applied six heatwave definitions (HD1-HD6) varying by duration (2 or 3 consecutive days or more) and thresholds (90th, 95th, 99th percentiles). We fitted Bayesian hierarchical Poisson models to estimate heatwave-mortality associations varying by space and time. We additionally adjusted for relative humidity and national. We then combined these estimates with probabilistic climate attribution methods to quantify the number and proportion of heatwave-related deaths attributable to human induced climate change. Results Heatwaves raised mortality consistently, with relative risks from 1.08 (95% CrI (Credible Interval): 1.07- 1.09; HD1) to 1.15 (1.11- 1.20; HD6). Risks increased with heatwave intensity and duration and peaked among females and adults aged 85 years and older. We did not detect a consistent temporal decline in risk or marked spatial heterogeneity. Human induced climate accounted for 51-94% of heatwave related deaths across definitions. The proportion attributable to climate change rose over time. Conclusions Heatwaves already impose a major mortality burden in Greece, with more than half driven by anthropogenic climate change and little evidence of population level adaptation. These findings call for rapid emissions reductions and targeted adaptation, including stronger heat health warning systems and protection of vulnerable groups.