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Dying from Heat and Cold in Australia
Volume 17, Number 39: 24 September 2014

Paper Reviewed
Bennett, C.M., Dear, K.B.G. and McMichael, A.J. 2014. Shifts in the seasonal distribution of deaths in Australia, 1968-2007. International Journal of Biometeorology 58: 835-8428.

In a paper published in the International Journal of Biometeorology, Bennett et al. (2014) say that "studies in temperate countries have shown that both hot weather in summer and cold weather in winter increase short-term (daily) mortality," suggesting to them that "the gradual warming, decade on decade, that Australia has experienced since the 1960s, might therefore be expected to have differentially affected mortality in the two seasons, and thus indicate an early impact of climate change on human health."

In response to this suggestion, we say right on! ... for in studying the ratio of summer to winter deaths against a background of rising average annual temperatures over a period of four decades in Australia, the three researchers from that country found that this summer/winter "death ratio" had increased from a value of 0.71 to 0.86 since 1968, due to summer deaths rising faster than winter deaths. And they add that "the same trend, albeit of varying strength, is evident in all states of Australia, in four age groups (aged 55 years and above) and in both sexes."

This phenomenon, as the three researchers report, "suggests that the change [the increase in summer/winter death ratio] has so far been driven more by reduced winter mortality [due to reductions in extreme cold] than by increased summer mortality [due to increases in extreme warmth]," as well as the fact that the greater number of typical winter-season deaths "is largely explained," in their words, "by infectious disease transmission peaks during winter and the exacerbation of chronic diseases, especially cardiovascular and respiratory conditions," citing Cameron et al. (1985). Also extremely important, we might add, it was found by Karl et al. (1984, 1991) that over the course of 20th-century global warming, daily minimum temperatures rose at a rate that was fully three times greater than the rate of daily maximum temperature over most of the world, so that the stress of extreme cold was reduced much faster than the stress of extreme heat was increased.

And so it can be concluded that with daily minimum temperatures rising so much faster than daily maximum temperatures all around the world, global warming - if it ever resumes after its nearly two-decade hiatus - should lead to less temperature-related mortality in most parts of the planet, as has historically been observed in Australia.

References
Cameron, A.S., Roder, D.M., Esterman, A.J. and Moore, B.W. 1985. Mortality from influenza and allied infections in South Australia during 1968-1981. Medical Journal of Australia 142: 14-17.

Karl, T.R., Jones, P.D., Knight, R.W., Kukla, G., Plummer, N., Razuvayev, V., Gallo, K.P., Lindseay, J., Charlson, R.J. and Peterson, T.C. 1984. A new perspective on recent global warming: asymmetric trends of daily maximum and minimum temperature. Bulletin of the American Meteorological Society 74: 1007-1023.

Karl, T.R., Kukla, G., Razuvayev, V.N., Changery, M.J., Quayle, R.G., Heim Jr., R.R., Easterling, D.R. and Fu, C.B. 1991. Global warming: evidence for asymmetric diurnal temperature change. Geophysical Research Letters 18: 2253-2256.