Background: Recent scientific developments made it possible to quantify the health impacts of climate change. However, limited health attribution studies have been conducted to date.
Objectives: We address limitations in existing methods using as case study an assessment of heat mortality attributable to human-induced climate change in the Canton of Zürich (Switzerland) over 50 years (1969-2018). We also quantify the effects of changes in vulnerability on heat-related mortality.
Methods: We use daily station observations, reanalysis data and an ensemble of climate models to derive timeseries of observed climate data, and counterfactual data that represent a world without human-induced climate change. We estimated the temperature-mortality relationship by conducting a time-series analysis using observed daily-mean temperature and mortality data. We quantified the heat-related mortality using the observed mortality and the mortality risk estimate corresponding to the mean temperature each day with the temperature of minimum mortality as reference, for the observed and counterfactual temperature series. To quantify the effects of changing exposure and vulnerability over time, we compared mortality in scenarios in which the exposure-response relationship derived for 1986-2003 is applied to 2004-2018 and in which the relationship is recalculated based on observed temperature and mortality over the period 2004-2018.
Results: We found nearly 1,700 deaths attributable to human-induced climate change between 1969-2018, and that changing vulnerability, probably due in part to adaptation, avoided at least 700 additional deaths in recent decades.
Discussion: Heat-related deaths occur through the summer months but peak during heatwaves. Our approach builds on existing epidemiological methods to shed light on the adverse effects of climate change on human health, and demonstrates the potential of effective adaptation measures to reduce the mortality burden of heat. The analyses described here could be adapted and applied elsewhere to quantify the effect of climate change on other health outcomes.