Projections of temperature-related excess mortality under climate change scenarios

Background: Climate change can directly affect human health by varying exposure to non-optimal outdoor temperature. However, evidence on this direct impact at a global scale is limited, mainly due to issues in modelling and projecting complex and highly heterogeneous epidemiological relationships across different populations and climates. Methods: We collected observed daily time series of mean temperature and mortality counts for all causes or non-external causes only, in periods ranging from Jan 1, 1984, to Dec 31, 2015, from various locations across the globe through the Multi-Country Multi-City Collaborative Research Network. We estimated temperature–mortality relationships through a two-stage time series design. We generated current and future daily mean temperature series under four scenarios of climate change, determined by varying trajectories of greenhouse gas emissions, using five general circulation models. We projected excess mortality for cold and heat and their net change in 1990–2099 under each scenario of climate change, assuming no adaptation or population changes. Findings: Our dataset comprised 451 locations in 23 countries across nine regions of the world, including 85 879 895 deaths. Results indicate, on average, a net increase in temperature-related excess mortality under high-emission scenarios, although with important geographical differences. In temperate areas such as northern Europe, east Asia, and Australia, the less intense warming and large decrease in cold-related excess would induce a null or marginally negative net effect, with the net change in 2090–99 compared with 2010–19 ranging from −1·2% (empirical 95% CI −3·6 to 1·4) in Australia to −0·1% (−2·1 to 1·6) in east Asia under the highest emission scenario, although the decreasing trends would reverse during the course of the century. Conversely, warmer regions, such as the central and southern parts of America or Europe, and especially southeast Asia, would experience a sharp surge in heat-related impacts and extremely large net increases, with the net change at the end of the century ranging from 3·0% (−3·0 to 9·3) in Central America to 12·7% (−4·7 to 28·1) in southeast Asia under the highest emission scenario. Most of the health effects directly due to temperature increase could be avoided under scenarios involving mitigation strategies to limit emissions and further warming of the planet. Interpretation: This study shows the negative health impacts of climate change that, under high-emission scenarios, would disproportionately affect warmer and poorer regions of the world. Comparison with lower emission scenarios emphasises the importance of mitigation policies for limiting global warming and reducing the associated health risks. Funding: UK Medical Research Council. © 2017 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 licenseThis work was primarily supported by the Medical Research Council-UK (grant MR/M022625/1). The following individual grants also supported this work: YG was supported by the Career Development Fellowship of Australian National Health and Medical Research Council (grant APP1107107); AT was supported by the Ministry of Education of Spain (grant PRX17/00705); VH was supported by the German Federal Ministry of Education and Research (grant 01LS1201A2); JK was supported by the Czech Science Foundation (grant 16-22000S); JJKJ and NRIR were supported by the Research Council for Health, Academy of Finland (grant 266314); MH, YLG, C-fW, YH, and HKi were supported by the Global Research Laboratory (grant K21004000001-10A0500-00710) through the National Research Foundation of Korea; YH was supported by the Environment Research and Technology Development Fund (S-14) of the Ministry of the Environment, Japan; YLG was supported by the National Health Research Institutes of Taiwan (grant NHRI-EM-106-SP03); and MLB was supported by a US Environmental Protection Agency Assistance Agreement awarded to Yale University (grant 83587101).Peer reviewe