USA: Air conditioning has been responsible for a dramatic decline in heat-related deaths in the USA over the last 50 years, according to a new report from the Massachusetts Institute of Technology (MIT).
Based on what the authors describe as the most comprehensive set of data files ever compiled on mortality and its determinants over the course of the 20th century, the report reveals that on days with a mean temperature exceeding 90°F mortality rates have declined by about 80% over the course of the 20th century in the USA, with almost the entire decline occurring after 1960.

Estimates suggest that during the period from 1960 to 2004, days with an average temperature exceeding 90°F, relative to a day in the 60°F-69°F range, lead to approximately 600 premature fatalities annually. If the temperature-mortality relationship from before 1960 still prevailed, there would have been about 3,600 premature fatalities annually from days with an average temperature exceeding 90°F.

The report points to the instaltion of air conditioning in domestic properties as the main cause of this dramatic reduction.

'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,' says the report. 'However, 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 90°F.

The fact that this report will pose a dilemma for those wishing to stop the proliferation of air conditioning on environmental grounds is not lost on the authors: 'Residential AC appears to be both the most promising technology to help poor countries mitigate the temperature related mortality impacts of climate change and, because fossil fuels are the least expensive source of energy, a technology whose proliferation will speed up the rate of climate change,' it says.