Human health threats spread by global warming

Newly published evidence showing the potent effect of global warming on human health is sure to stir controversy. One potentially touchy aspect of the new findings is that they hinge at least in part on new analyses of previously published data using more rigorous statistically techniques that in some cases have reversed the older findings.

Researchers from Emory University in the US and Wageningen University in the Netherlands looked at over 70 major studies that compared the spread of malaria to global warming. Their conclusion: Global warming is a significant contributor to the spread of the disease. Malaria is a major human health scourge, infecting 250 million and killing 1 million each year. Since the mosquitoes and parasite that transmit malaria are highly sensitive to changes in temperature, climate has historically helped to isolate the disease in warm, tropical areas of Africa, South America and South Asia. The past 40 years, however, have seen the slow progression of the disease into highland regions previously deemed too chilly for this unwelcome traveler, including East Africa, Indonesia and Afghanistan.

Previous literature reviews had not always found that regions newly infiltrated by malaria were experiencing warming trends. A 2002 study of the Kericho highlands of Kenya, for example, reported no warming trend despite the recent arrival of malaria. This new review, however, reanalyzed the Kenyan data set, and found statistically significant warming even after using three different statistical tests.

The authors note that climate change is not the only cause for the disease spread. Migration, and changes in land use, agriculture and farming practices all likely contribute as well. But when combined with even subtle warming trends, the results in terms of human health cost may equal much more than the sum of each separate change. Climate data has proven tricky to quantify in terms of the risks it poses, and trickier still to communicate in he super-heated environment of global politics. But falling on the heals of recent controversies surrounding the use of potentially bogus data by climate scientists, this new study is particular interesting in that it appears to be overturning previous climate-related findings by increasing statistical rigor. In fact, the authors found that in general the most rigorous of the studies they reviewed linked climate change to malaria spread, and the least rigorous were the ones finding no link.

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