Adaptation to Heat and Cold in the Context of a Changing Climate: A Multi-Country Analysis

Abstract

Background/Aim: The net impact of global warming will depend on the extent to which adaptation overcomes the effect of gradual changes in temperature. Disentangling the two processes is critical to provide accurate projections of future temperature-related impacts under climate change scenarios. We present evidence from a multi-country investigation that assessed temporal trends in mortality attributed to both heat and cold, and adaptation. Methods: We collected data from 305 locations in 10 countries between 1985 and 2012. Temporal trends in country-specific attributable mortality fractions (AF) for heat/cold (temperatures above/below minimum mortality temperature) were estimated using a two-stage time series design with time-varying distributed lag non-linear models and multivariate meta-analysis. To disentangle the contribution of adaptation from changes in attributable mortality due to gradual increases in temperature, we compared yearly AF with those predicted assuming either temperature distribution or exposure-response relationships as constant across the study period, respectively. Results: Heat-AF decreased in all countries except Australia and United Kingdom, from 0.45-1.39% in the first to 0.15-0.93% in the last 5-year periods, respectively. Different patterns were found for cold, with ranges from 5.56-15.43% to 2.17-8.54%, showing either decreasing (Japan, Spain, Australia, Ireland), increasing (US), or stable trends (Canada, South Korea, United Kingdom). We found inconsistent patterns in Brazil and Switzerland and a null heat-impact in Ireland. Long-term trends were mostly captured by temporal variation in exposure-response associations (interpreted as adaptation), while year-to-year fluctuations were driven by changes in temperature distribution. Conclusions: Our findings indicate that heat-mortality impacts decreased in most countries consistent with previous studies, whereas cold-mortality exhibited heterogeneous trends. In addition, the pace of adaptation has been faster than the observed warming, suggesting there is scope for the implementation of effective public health policies under climate change. Further investigations should focus on identification of the factors responsible for these adaptation trends.