Net impact of air conditioning on heat-related mortality in Japanese cities

Background: Air conditioning (AC) presents a viable means of tackling the ill-effects of heat on human health. However, AC releases additional anthropogenic heat outdoors, and this could be detrimental to human health, especially in urban communities. This study determined the excess heat-related mortality attributable to anthropogenic heat from AC use under various projected global warming scenarios in seven Japanese cities. The overall protection from AC use was also measured. Methods: Daily average 2-meter temperatures in the hottest month of August from 2000 to 2010 were modeled using the Weather Research and Forecasting (WRF) model with BEP+BEM (building effect parameterization and building energy model). Risk functions for heat–mortality associations were generated with and without AC use from a two-stage time series analysis. We coupled simulated August temperatures and heat–mortality risk functions to estimate averted deaths and unavoidable deaths from AC use. Results: Anthropogenic heat from AC use slightly augmented the daily urban temperatures by 0.046 °C in Augusts of 2000–2010 and up to 0.181 °C in a future with 3 °C urban warming. This temperature rise was attributable to 3.1–3.5 % of heat-related deaths in Augusts of 2000–2010 under various urban warming scenarios. About 36–47 % of heat-related deaths could be averted by air conditioning use under various urban warming scenarios. Discussion: AC has a valuable protective effect from heat despite some unavoidable mortality from anthropogenic heat release. Overall, the use of AC as a major adaptive strategy requires careful consideration.