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Cold-Related Mortality in Europe
Analitis, A., Katsouyanni, K., Biggeri, A., Baccini, M., Forsberg, B., Bisanti, L., Kirchmayer, U., Ballester, F., Cadum, E., Goodman, P.G., Hojs, A., Sunyer, J., Tiittanen, P. and Michelozzi, P. 2008. Effects of cold weather on mortality: Results from 15 European cities within the PHEWE project. American Journal of Epidemiology 168: 1397-1408.

The fourteen authors of this major assessment of cold-weather effects on mortality in Europe introduce their study by stating that "in recent years, the effects of meteorologic factors on health have attracted renewed interest because of the observed and predicted climate change, which is expected to result in a general rise in temperature." And this development, in their words, has led to a "recent focus on heat-wave episodes," which may have fostered the perception that cold-related mortality is not as important a public health concern as is heat-related mortality.

What was done
To rectify this situation, Analitis et al. analyzed short-term effects of cold weather on mortality in 15 European cities (Athens, Greece; Barcelona, Spain; Budapest, Hungary; Dublin, Ireland; Helsinki, Finland; Ljubljana, Slovenia; London, United Kingdom; Milan, Italy; Paris, France; Prague, Czech Republic; Rome, Italy; Stockholm, Sweden; Turin, Italy; Valencia, Spain; Zurich, Switzerland). More specifically, they assessed the effects of minimum apparent temperature on cause- and age-specific daily mortality over the cold half of the year (October-March), using data from 1990-2000 that they analyzed via "Poisson regression and distributed lag models, controlling for potential confounders."

What was learned
The international team of scientists -- hailing from Finland, Greece, Ireland, Italy, Slovenia, Spain and Sweden -- found that "a 1C decrease in temperature was associated with a 1.35% increase in the daily number of total natural deaths and a 1.72%, 3.30% and 1.25% increase in cardiovascular, respiratory, and cerebrovascular deaths, respectively." In addition, they report that "the increase was greater for the older age groups," and that the cold effect "persisted up to 23 days, with no evidence of mortality displacement [our italics]."

What it means
The fact that Analitis et al. say that "no mortality displacement was observed" in the case of cold-related deaths in Europe is most important, because in the case of heat-related deaths there is such a displacement, and its impact is huge.

In Germany, for example, Laschewski and Jendritzky (2002) analyzed daily mortality rates in Baden-Wurttemberg (10.5 million inhabitants) over the 30-year period 1958-97 to determine the sensitivity of the population of this moderate climatic zone to long- and short-term episodes of heat and cold. Their research indicated that mortality shows "a marked seasonal pattern with a minimum in summer and a maximum in winter." With respect to short-term exposure to heat and cold, however, they found that "cold spells lead to excess mortality to a relatively small degree, which lasts for weeks," and that "the mortality increase during heat waves is more pronounced, but is followed by lower than average values in subsequent weeks," which suggests, in their words, that people who died from short-term exposure to heat "would have died in the short term anyway."

With respect to this short-term mortality displacement that occurs in conjunction with heat-related deaths, Laschewski and Jendritzky's data demonstrate that it is precisely that, i.e., merely a displacement of deaths and not an overall increase. They found, for example, that the mean duration of above-normal mortality for the 51 heat episodes that occurred from 1968 to 1997 was 10 days, with a mean increase in mortality of 3.9%, after which there was a mean decrease in mortality of 2.3% for 19 days. Hence, the net effect of the two perturbations was actually an overall decrease in mortality of 0.2% over the full 29-day period. Consequently, it should be abundantly clear that cold spells are much more deadly than heat waves, and that we could thus expect global warming to confer significant benefits upon mankind by significantly reducing the very real killing power of routine bouts of colder-than-normal weather.

And thus it is that Analitis et al. conclude their paper by stating that their results "add evidence that cold-related mortality is an important public health problem across Europe and should not be overlooked by public health authorities because of the recent focus on heat-wave episodes."

Laschewski, G. and Jendritzky, G. 2002. Effects of the thermal environment on human health: an investigation of 30 years of daily mortality data from SW Germany. Climate Research 21: 91-103.

Reviewed 4 March 2009