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SO2, CO, Smoke or Low Temperature: Which Kills More?
Keatinge, W.R. and Donaldson, G.C. 2001. Mortality related to cold and air pollution in London after allowance for effects of associated weather patterns. Environmental Research 86: 209-216.

What was done
The authors studied the effects of temperature, wind, rain, humidity and sunshine during high pollution days in the greater London area over the period 1976-1995 to determine what weather and/or pollution factors have the biggest influence on human mortality.

What was learned
Simple plots of mortality rate versus daily air temperature revealed a linear increase as temperatures fell from 15C to near 0C. Mortality rates at temperatures above 15C were, in the words of the authors, "grossly alinear," showing no trend. Days with high SO2, CO or PM10 concentrations were colder than average, but a multiple regression analysis revealed that none of these pollutants was associated with a significant increase in mortality among those 50+ years of age. Indeed, only low temperatures were shown to have a significant effect on both immediate (1 day after the temperature perturbation) and long-term (up to 24 days after the temperature perturbation) mortality rates. The net increase in mortality over a 24-day period following a 1-day fall in temperature was 2.77 daily deaths per million people per degree Celsius.

Why are cold temperatures so deadly? The authors say it is because "cold causes mortality mainly from arterial thrombosis and respiratory disease, attributable in turn to cold-induced hemoconcentration and hypertension and respiratory infections."

What it means
Given the large amount of data examined and the types of analyses conducted, the authors conclude they have "confirmed that the large, delayed increase in mortality after low temperature is specifically associated with cold and is not due to associated patterns of wind, rain, humidity, sunshine, SO2, CO, or smoke."

Yes, cold kills. Perhaps we should all pray for a little global warming as an antidote.