WASHINGTON -- As winter begins to tighten its grip on much of the United States, air conditioning doesn't seem like much of a survival strategy. But a new study that included researchers from Carnegie Mellon University has found that home air conditioning played a key role in reducing American death rates over the past half-century, by keeping people cool on extremely hot days.
The installation of air conditioning in American homes is the reason why the chances of dying on an extremely hot day fell 80 percent over the past half-century, according to an analysis by a team of American researchers.
The findings, based on a comprehensive analysis of U.S. mortality records dating back to 1900, suggest that the spread of air conditioning in the developing world could play a major role in preventing future heat-related deaths linked to climate change. Very few U.S. homes had air conditioning before 1960; by 2004, that figure had climbed to 85 percent.
A team of researchers from Carnegie Mellon, Tulane University, the National Bureau of Economic Research and the Massachusetts Institute of Technology examined patterns in heat-related deaths between 1900 and 2004. The group found that days where temperatures rose above 90 degrees Fahrenheit accounted for about 600 premature deaths annually between 1960 and 2004 period, one-sixth as many as would have occurred under pre-1960 conditions.
"It's all due to air conditioning," said MIT environmental economics professor Michael Greenstone, one of the paper's co-authors, adding that factors including increased electrification and health care access did not affect heat-related death.
The likelihood of a premature death on an extremely hot day between 1929 and 1959 was 2.5 percent, the academics found, dropping to less than 0.5 percent after 1960. The paper is under review at an academic journal.
Matthew Kahn, an economics and public policy professor at the University of California, Los Angeles' Institute of Environment, called the study "a very strong paper" that could show one strategy for adapting to increasingly frequent bouts of warmer weather. The United Nations Intergovernmental Panel on Climate Change issued a report this year linking the increase in heat waves to human-generated greenhouse gas emissions, predicting the frequency of these events will increase in the coming decades.
The study's results could be particularly important for nations such as India, where only a small portion of the population has residential air conditioning. The typical person in India experiences 33 days per year where the temperature rises above 90 degrees Fahrenheit; this could increase by as much as 100 days by the end of the century, according to some climate projections.
The spread of air conditioning has one obvious problem, Mr. Greenstone noted, since many of these units will likely be powered by fossil fuels and will therefore increase the world's carbon output.