Enduring the Heat: Could residential air conditioning mitigate the danger of global climate change?

With the onset of climate change, it is feared that the hot summers of yesterday have become the average summer today. Hundreds of thousands of people, especially those who live in climate-vulnerable countries, might suffer from extreme hot weather associated with global warming. As climate change poses an ever greater threat on people’s well-being, individuals and nations are searching for ways to tackle this global problem. In “Adapting to Climate Change: The Remarkable Decline in the U.S. Temperature-Mortality Relationship over the 20th Century,” Alan Barreca et al. find that the adoption of air conditioning in homes is associated with the substantial decline in the US temperature-mortality relationship over the 20^th century. They estimate that the US experienced an 80 percent reduction in the mortality rate to high temperatures over this period.

The paper begins by exploring the reasons for the declining temperature-mortality relationship. Three major public health innovations are studied. First, access to health care leads to better treatment of heat-related illnesses. Second, increased access to electricity enables a variety of innovations, including indoor plumbing, fans, and refrigerators. Third, the adoption of air conditioning reduces the stress of people’s thermoregulatory systems in extreme hot weather.

After the conceptual analysis, Barreca et al. construct an empirical model and examine the impact of those determinants on the decline in heat-related mortality rates. The paper collected a comprehensive set of data on mortality rates, temperature, doctors per capita, access to electricity, and residential air conditioning. In order to purge permanent differences in mortality across states and standardize the national data across different seasons, Barreca et al. adopted baseline specifications that include state-by-month fixed effects and year-by-month fixed effects.

Barreca et al. make two primary discoveries from their empirical analysis. First, the US experienced a substantial decline in the heat-related mortality rate over the 20^th century. The impact of hot weather, defined as over 90 degrees Fahrenheit, on mortality rate declined by about 80 percent between the periods of 1900-1959 and 1960-2004. Whereas the US experienced approximately 3,600 premature deaths on hot weather days in the 1900-1959 period, the 1960-2004 period only saw 600 deaths per year from the temperature-mortality relationship. Second, the adoption of residential air conditioning is associated with almost the entire decline in heat-related mortality rates, while access to health care and electricity do not reduce the temperature-mortality relationship significantly.

In order to apply this finding, Barreca et al. also examine the similarities between the US in the 20^th century and many developing countries today. They turn out to be similar in many aspects such as life expectancies, infant mortality rates, and residential air conditioning penetration rates.

Currently, India and Indonesia are expected to be disproportionately affected by climate change, and only a few individuals in these countries have access to residential air conditioning. Under global warming, temperature in those already hot countries is expected to rise to an even higher level. This paper shows that adoption of residential air conditioning might be an effective way to survive the hot weather and mitigate the dangerous impacts of climate change in nations such as these.

Feature Photo: cc/(JSsocal)