What was done
The authors examined trends in U.S. death rates over the period 1979-97 due to excessive hot and cold weather conditions.

What was learned
Over the 18-year study period, there were no trends in deaths due to either extreme heat or cold in the entire population or, "more remarkably," as the authors say, in the older more susceptible age groups, i.e., those aged 65 and over, 75 and over, and 85 and over.  However, deaths due to extreme cold exceeded those due to extreme heat by 80% to 125%.

What it means
With respect to the absence of trends in U.S. death rates attributable to either extreme heat or cold, the authors state that this observation "suggests that adaptation and technological change may be just as important determinants of such trends as more obvious meteorological and demographic factors."  Then, again, it could also mean that there has been no real trend in either extreme heat or cold in the United States between 1979 and 1997, which, as we noted in a previous editorial (The Global Surface Air Temperature Record Must Be Wrong), may well be a real possibility.  In any event, it is clear, for the United States at least, that extreme cold is a much more important cause of death than is extreme heat, suggesting that if a real warming ever were to occur, it would likely eliminate many more deaths due to cold than it would increase deaths due to heat, producing a net reduction in deaths due to extreme temperatures of both types.