March 14, 2007

Lower Mortality Thanks to Global Warming?

The release of the Summary for Policymakers of the Intergovernmental Panel on Climate Change (IPCC), sent the media into a global warming frenzy. Headlines were literally predicting “climate chaos” in the coming decades, humanity and every specie on the planet are in deep peril, and according to an international group of celebrities (the “Global Cool” crowd), we have “10 years to save the planet.”

Among the usual claims, we learn that many humans will die as the temperature of the Earth increases, and that the elderly, the children, and the poorest among us are most at risk. Throw in a few pictures of Paris during the 2003 European heat wave, claim tens of thousands died in that event, and the icing is on the cake. A Google search of “Global Warming and Mortality” will lead you to 723,000 different sites – we sampled a dozen or so, and according to these sites, you will be lucky to survive much longer if temperatures continue to rise.

We have addressed the serious scientific literature on global warming and human mortality many times in the past at World Climate Report, and an article has been published in a recent issue of the International Journal of Biometeorology that will surely not be featured by the popular media (as you will see, maybe it will be featured based on one interesting finding). The title alone “Temperature-related mortality in France, a comparison between regions with different climates from the perspective of global warming” tells us immediately that someone has something credible to say about global warming and human mortality in France. The article is especially timely given the focus we see in so many global warming presentations on the thermal conditions in Paris during the summer of 2003.

The research team from various institutions in France collected daily temperature and mortality data from 1991-1995 for six “departments” (a.k.a., states or counties) located in urban, oceanic, semi-continental, mountain, and two different Mediterranean settings (Figure 1). They broke the data into three age groups including less than 1 year old, 1 to 64 years old, and greater than 64 years old. They also divided the data by sex and by major causes of death including respiratory disease, cerebrovascular disease or stroke, heart disease, and other diseases of the circulatory system. Violent deaths resulting from murder or accidents were excluded from their study.

Figure 1. Study areas in France. Departments: 1 Paris (urban), 2 Finistère (oceanic), 3 Côte-d’Or (semi-continental), 4 the Hautes-Alpes (mountain), 5 the Alpes-Maritimes (mild and sheltered Mediterranean), and 6 the Hérault (extreme and windy Mediterranean)

The Laaidi et al. team found for the whole population, “As expected, temperature and daily deaths exhibited a marked temporal pattern. For all the departments investigated, mean daily counts of deaths showed an asymmetrical V-like or U-like pattern with higher mortality rates at the time of the lowest temperatures experienced in the area than at the time of the highest temperatures. The lowest temperatures ranged between approximately −9°C in the North of the country and approximately −2°C in the South, while the highest peak reached 24°C in the North and 30°C in the South.” The data clearly show that people adjust to their environment and people in cold areas are more susceptible to warm temperatures and people living in warm areas are more susceptible to cold temperatures (Figure 2). A thermal band exists called the thermal optimum in which mortality is low, and the scientists note that “The level of the thermal optimum rises in line with the warmer climatic conditions of each department. The thermal optimum is greater in Paris, probably due to the urban heat island, than in the Hérault, which is situated in the extreme south of France in a Mediterranean climate.”

Figure 2. Daily mean mortality in 3°C temperature bands in Paris, the Hérault, Finistère, the Hautes-Alpes, Côte-d’Or and the Alpes-Maritimes for the whole population (1991–1995) and per 100,000 Inhabitants (from Laaidi et al., 2006)

We did find one result of potential interest to global warming advocates the world over. Laaidi et al. note that “The thermal optimum was consistently lower for women, especially those over 64.” So instead of simply stating that global warming will disproportionably impact children, elderly, and the poor, we can now announce that women, particularly older women, could be in more peril than men should the temperatures rise. If this article gets any popular press coverage, this is sure to be the angle – grandmothers beware of global warming!

Actually, with respect to any temperature rise due to global warming, the research team found “For both men and women mortality was higher at low temperatures, suggesting a lesser ability to adapt to the cold.” Based on another related study, they state “In England and Wales, the higher temperatures predicted for 2050 might result in nearly 9,000 fewer winter deaths each year.” Laaidi et al. conclude “our findings give grounds for confidence in the near future: the relatively moderate (2°C) warming predicted to occur in the next half century would not increase annual mortality rates.”

Numerical models of climate consistently predict warming in winter in mid-latitude locations such as France and less warming in the summer months given the buildup of greenhouse gases. The Laaidi et al. study and dozens of other similar studies show that the threat to human mortality lies on the cold end of the thermal spectrum rather than the warm end. Higher temperatures in the winter would certainly decrease mortality, and we could conclude from this and other studies that in terms of temperature-related mortality, global warming would save lives – a message not well conveyed in the hundreds of thousands of websites on the subject.


Laaidi, M., K. Laaidi, and J.-P. Besancenot, 2006. Temperature-related mortality in France, a comparison between regions with different climates from the perspective of global warming. International Journal of Biometeorology, 51, 145-153.

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