Heat- and cold-related deaths under two climate change scenarios in Stockholm, Sweden+C45

Background: Climate change is projected to result in heat events increasing and cold events decreasing.  This will have substantial impact on human health, particularly when compounded with demographic change. A novel technique, the Spatial Synoptic Classification (SSC), categorizes daily weather into one of seven types based on several meteorological variables. Previous studies have shown the association of hot and cold weather types with mortality. Here we estimated future mortality due to extremely hot and cold weather types under different climate change scenarios for Stockholm, Sweden.

Methods: Time-series Poisson regression with distributed lags was used to assess the relationship between extremely hot and cold weather events (defined by the SSC) and daily deaths in the population above 65 years, with effects cumulated over 6 days in summer and 28 days in winter from 1991 to 2014. A global climate model (MPI-M-MPI-ESM-LR) and two climate change scenarios (RCP 4.5 and 8.5) were used to assess the occurrence of future hot and cold days in Stockholm, Sweden from 2031 to 2070. Attributable fractions (AF) and numbers of heat- and cold related deaths with 95% confidence intervals (CI) were estimated.

Results: For the RCP 4.5 scenario, the mean annual deaths attributed to heat raised from 48.7 (CI 32.2-64.2; AF=0.68%) in the period 2031-2040 to 90.2 (56.7-120.5; AF=0.97%) in 2061-2070, respectively. However, for the RCP 8.5 scenario, the heat related deaths showed a more drastic increase from 52.1 (33.6-69.7; AF=0.72%) to 126.4 (68.7–175.8; AF=1.36%) between the first and the last decade. Cold related deaths slightly increased over the projected period in both scenarios.Conclusions: Results show a progressive increase of heat related mortality in terms of attributable numbers and fractions, and a reduction of cold related deaths. With an increasing elderly population, heat-related mortality will outweigh the cold-related mortality at least under the RCP 8.5 scenario