Counteracting increased heat-related mortality through adaptation: a quantitative assessment in a multi-country multi-city setting.

Background & aims: Climate change is exacerbating the current heat-related health burden and will continue to do so at a higher speed in the coming decades if no adaptation occurs. Although previous studies have suggested potential paths of adaptation, there is little quantitative evidence on the degree of adaptation needed to counteract the increased heat-related mortality under different climate change scenarios. Methods: We performed a health impact projection analysis using observed data on 451 locations in 23 countries included in the MCC database and modelled temperature from 3 global circulation models (CMIP5 - ISMIP2b). For each city, we combined present-time risk functions, represented by the exposure-response association obtained from a two-stage time series analysis of the observed temperature-mortality data, with projected daily temperature in 20-year warming scenarios consistent with an increase in global mean temperature of 2, 3 and 4ºC from the preindustrial period. Using a novel optimization method, we estimated a risk reduction factor to be applied to the present-time exposure-response association representing the level of adaptation needed to counteract the increased heat-mortality burden under each warming target. Results: Assuming constant vulnerability and population, climate change would progressively amplify heat-related mortality reaching 3.9% (95%CI:0.6;0.9) of all-cause mortality due to heat at 4ºC warming scenario (vs. 0.4% (0.2-0.6) in baseline 1986-2005). To counteract the impact of the progressive increase of temperatures, present-time heat-related risks should reduce on average by 70% (35;104), 84% (60;104) and 91% (80;103) under the 2, 3 and 4ºC scenarios, respectively. Conclusions: Our preliminary findings show that substantial reductions in vulnerability would be required to counteract the increase in heat-mortality burden driven by climate change. Further steps will aim to extend the current analysis over a larger sample of locations and consider scenarios of population development. Keywords: climate change, adaptation, heat, mortality, projections, methods.