Quantifying the contributions of climate change and adaptation to mortality from unprecedented extreme heat events

We revisit the August 2003 heat wave in France to better understand the influences of climate change and human adaptation on mortality from unprecedented extreme heat events. We reconfirm previous findings of approximately 16,000 excess deaths during the event, but show that standard heat–mortality exposure–response functions underestimate this death toll by 55% in an out-of-sample test. Using an exposure–response function accounting for consecutive hot days that more effectively predicts mortality in 2003, we attribute more than 6,000 deaths in August 2003 to climate change. Additionally, we show that the heat–mortality relationship has moderated since 2003. As a result, we project future 2003-like events to cause 77% fewer deaths in France compared to a world without that moderation.