Global warming may not reduce winter deaths

Contrary to popular assumptions, global warming may not lead to substantial reduction in winter deaths, a study says.

Warming climate trend has led to reductions in cold-related mortality than some experts have anticipated, the results showed.

Among 39 cities in the US and France that the researchers studied, there was no evidence that cities having warming temperatures experienced any less winter mortality than did cooler cities.

"Some have claimed that warmer winters due to climate change will lead to big reductions in winter deaths. Our work suggests that this is unlikely to be the case," said Columbia University's Patrick Kinney, lead author on the recent report from the Intergovernmental Panel on Climate Change.

If cold temperatures were directly responsible for winter mortality rates, then we would expect future warming to lead to substantial reductions in winter mortality, Kinney said.

On the other hand, "climate warming would have little benefit if seasonal factors other than temperature are mainly responsible for winter excess mortality."

To determine whether and to what extent cold temperatures affect excess winter mortality, Dr. Kinney and colleagues analysed temperature and mortality data from 36 US cities and Paris, Lyon and Marseille in France.

Mortality rates were obtained from the US National Centre for Health Statistics and the French National Institute for Statistics and Economics Studies for the period 1971-2007.

Results showed that cities with warmer winters have similar rates of winter deaths compared to their colder winter-counterparts and that there was little relationship evident between mortality and cold temperatures.

"These cities vary widely in demography, urban design and socio-cultural background, all of which might influence exposure to outdoor temperature and related mortality risks," Kinney said.

The lack of correlation between seasonal temperature differences and winter season excess mortality suggests that other seasonal factors are driving winter excess mortality including lack of exercise, low humidity and time spent indoors which may lead to increased risk of flu and other respiratory infections and its complications.

This study appeared in the journal Environmental Research Letters.