Projections of temperature-attributable suicide under climate change scenarios in Japan

Abstract

BACKGROUND AND AIM: Recent studies have projected all-cause mortality attributable to non-optimal temperature under climate change scenarios. However, the impact of climate change on mental health remains to be assessed. The short-term association between suicide and temperature has been reported, but there is a lack of future projections of temperature-attributable suicide. We projected the excess temperature-related suicide mortality in Japan under three climate change scenarios until the 2090s. METHODS: Daily time series of mean temperature and the number of suicide deaths in 1973-2015 were collected for 47 prefectures in Japan. A two-stage time-stratified case-crossover analysis was used to estimate the temperature-suicide association. We obtained the modeled daily temperature series using five general circulation models (GCMs) under three climate change scenarios from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) Shared Socioeconomic Pathways scenarios (SSPs): SSP1-2.6, SSP2-4.5, and SSP5-8.5. We projected the excess temperature-related suicide mortality until 2099 for each scenario and evaluated the net relative changes compared with the 2010s. RESULTS: During 1973-2015, there was a total of 1,049,592 suicides in Japan. Net increases in temperature-related excess suicide mortality were estimated under all scenarios, with the highest increase under the high-emission scenario (SSP5-8.5). The net change in 2090-99 compared with 2010-19 was 0.6% (95% empirical confidence interval [eCI]: 0.1, 1.6) for a low emission scenario (SSP1-2.6), 1.3% (95% eCI: 0.6, 2.4) for an intermediate scenario (SSP2-4.5), and 2.4% (95% eCI: 0.7, 3.9) for a high emission scenario (SSP5-8.5). The increases were greater the higher the emission scenarios were. The increase in excess temperature-related suicide mortality was minimized under the SSP1-2.6 scenario assuming mitigation strategies. CONCLUSIONS: The comparison of projection results under different scenarios underscores the importance of mitigation, with the higher the emissions, the greater impact on the temperature-related suicide mortality. Keywords:Climate change, non-optimal temperature, mental health, projections, DLNM