This paper combines panel data on monthly mortality rates of US states and daily temperature variables for over a century (1900-2004) to explore the regional evolution of the temperature-mortality relationship and documents two key findings. First, the impact of extreme heat on mortality is notably smaller in states that more frequently experience extreme heat. Second, the difference in the heat-mortality relationship between hot and cold states declined over 1900-2004, though it persisted through 2004. Continuing differences in the mortality consequences of hot days suggests that health motivated adaptation to climate change may be slow and costly around the world.

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 807F 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).