Assessing mortality risk from heat stress due to global warming

With gradually progressing climate change in the future, the frequency and scale of hot summers like those observed in various places around the world in recent years will undoubtedly increase, giving rise to strong concerns over increased risk of death due to heat stress. Based on this background, we have developed a method to assess future changes in mortality due to heat stress with the entire globe as the target, and performed trial calculations using this method. The purpose of this report is to draw people's attention to the possible severe consequences of climate change by presenting the severest estimates in the uncertainty range due to adaptation/acclimation expected in the future, so as to induce further analysis and discussion on policies and measures. For the trial calculations, future changes in temperature were derived from the results of simulation using an Atmosphere-Ocean General Circulation Model with the highest spatial resolution in the world at the time of the study. Population densities were assumed not to alter in the future. Assuming that no adaptation or acclimation takes place, when the rates of change of excess mortality due to heat stress are examined by country, the results of our calculations show increases of approximately 100% to 1000%. It is confirmed that the burden of climate change impact is quite unequal among countries, at least from the viewpoint of heat stress mortality. When considered together with present population densities, significant increases in excess mortality density can be seen in China, India, and Europe. These regions are characterized by large losses due to climate change in absolute quantitative terms. The need to consider the adoption of adaptation measures is therefore most urgent in these regions.