Quantifying the Mortality Consequences of Climate Change : Evidence from Japan

Climate change is projected to increase global temperature and bring about more frequent and intense extreme events including compound extreme events with especially large damage to communities. This paper examines the mortality consequences of climate change across 22 climate change indicators that capture not only shifts in the mean and extremes of weather conditions, but also the amplification of weather extremes when they co-occur and interact in compound extreme events. Using data from 1718 Japan municipalities in 1980-2019, I identify the leading climate drivers of mortality in Japan and quantify the climate-mortality relationship drawing on model specifications selected by LASSO. In addition to temperature, relative humidity, precipitation, and humidity amplification in heat-and-humidity extremes all have significant impacts on mortality, with larger, non-linear effects at the heat extremes of the temperature distribution and both high and low extremes of relative humidity. The mortality responses to heat are concentrated in urban municipalities with no evidence of adaptation between early and late periods of climate change, whereas the mortality responses to humidity amplification are stronger in rural municipalities and fully concentrated in the early period of climate change. Over the study period in 1980-2019, the average municipality in Japan experienced a cumulative mortality of 120 deaths per 10,000 individuals from climate change, of which increases in temperatures contributed 129 deaths, increases in humidity amplification contributed 26 deaths, reductions in precipitation contributed 7 deaths, and reductions in relative humidity lowered mortality by 43 deaths.