Adapting to Climate Change: The Remarkable Decline in the U.S. Temperature-Mortality Relationship over the 20th Century
This paper examines the temperature-mortality relationship over the course of the twentieth-century United States both for its own interest and to identify potentially useful adaptations for coming decades. There are three primary findings. First, the mortality impact of days with mean temperature exceeding 80°F declined by 75 percent. Almost the entire decline occurred after 1960. Second, the diffusion of residential air conditioning explains essentially the entire decline in hot day–related fatalities. Third, using Dubin and McFadden’s discrete-continuous model, the present value of US consumer surplus from the introduction of residential air conditioning is estimated to be $85–$185 billion (2012 dollars). […]
Using the most comprehensive set of data files ever compiled on mortality and its determinants over the course of the 20th century in the United States or any other country, this paper makes two primary discoveries about mortality during the 20th century. First, we document a remarkable decline in the mortality effect of temperature extremes: The impact of days with a mean temperature exceeding 80° F has declined by about 70% over the course of the 20th century in the United States, with almost the entire decline occurring after 1960. The result is that there are about 14,000 fewer fatalities annually than if the pre-1960 impacts of mortality still prevailed. Second, the empirical results point to air conditioning as a central determinant in the reduction of the mortality risk associated with high temperatures during the 20th century. Specifically, the diffusion of residential air-conditioning after 1960 is related to a statistically significant and economically meaningful reduction in the temperature-mortality relationship at high temperatures. Indeed, the adoption of residential air conditioning explains essentially the entire decline in the relationship between mortality and days with an average temperature exceeding 80 °F. In contrast, we find that electrification (represented by residential electrification) and access to health care (represented by doctors per capita) are not statistically related to changes in the temperature mortality relationship.