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Global Warming and Malaria
Gething, P.W., Smith, D.L., Patil, A.P., Tatem, A.J., Snow, R.W. and Hay, S.I. 2010. Climate change and the global malaria recession. Nature 465: 342-345.

The authors say that based on "model predictions," it is "reported widely in global climate policy debates that climate change is adding to the present-day burden of malaria and will increase both the future range and intensity of the disease," citing the IPCC (2007) and the U.S. Environmental Protection Agency (2010).

What was done
Noting "it has long been known that the range of malaria has contracted through a century of economic development and disease control (Hay et al., 2009)," when "global temperature increases have been unequivocal," Gething et al. explore this seeming incongruity "for the first time," by comparing "an evidence-based map of contemporary malaria endemicity (Hay et al., 2009)" with "the most reliable equivalent for the pre-intervention era, around 1900 (Lysenko et al., 1968)," when malaria was "at its assumed historical peak," providing thereby a comparison of "the magnitude of observed changes in range and endemicity to those proposed to occur in response to climate change [italics added]."

What was learned
The six scientists -- hailing from the Spatial Ecology and Epidemiology Group, the Malaria Public Health and Epidemiology Group, and the Centre for Tropical Medicine of the UK's University of Oxford, plus the Departments of Biology and Geography and the Emerging Pathogens Institute of the United States' University of Florida -- report that "comparison of the historical and contemporary maps revealed that endemic/stable malaria is likely to have covered 58% of the world's land surface around 1900 but only 30% by 2007," and that "even more marked has been the decrease in prevalence within this greatly reduced range, with endemicity falling by one or more classes in over two-thirds of the current range of stable transmission." Hence, they state that "widespread claims that rising mean temperatures have already led to increases in worldwide malaria morbidity and mortality are largely at odds with observed decreasing global trends in both its endemicity and geographic extent." In fact, they report that "the combined natural and anthropogenic forces acting on the disease throughout the twentieth century have resulted in the great majority of locations undergoing a net reduction in transmission between one and three orders of magnitude larger than the maximum future increases proposed under temperature-based climate change scenarios."

What it means
Gething et al. conclude that there has been "a decoupling of the geographical climate-malaria relationship over the twentieth century, indicating that non-climatic factors have profoundly confounded this relationship over time," and they say that "non-climatic factors, primarily direct disease control and the indirect effects of a century of urbanization and economic development, although spatially and temporally variable, have exerted a substantially greater influence on the geographic extent and intensity of malaria worldwide during the twentieth century than have climatic factors." As for the future, therefore, they write that climate-induced effects "can be offset by moderate increases in coverage levels of currently available interventions."

Hay, S.I., Guerra, C.A., Gething, P.W., Patil, A.P., Tatem, A.J., Noor, A.M., Kabaria, C.W., Manh, B.H., Elyazar, I.R.F., Brooker, S., Smith, D.L., Moyeed, R.A. and Snow, R.W. 2009. A world malaria map: Plasmodium falciparum endemicity in 2007. PLoS Medicine 6: 10.1371/journal.pmed.1000048.

Intergovernmental Panel on Climate Change. 2007. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Parry, M.L., Canziani, O.F., Palutikof, J.P., van der Linden, P.J. and Hanson, C.E. (Eds.) Cambridge University Press.

Lysenko, A.J. and Semashko, I.N. 1968. In: Lebedew, A.W. (Ed.) Itogi Nauki: Medicinskaja Geografija, Academy of Sciences, Moscow, Russia, p. 25-126.

U.S. Environmental Protection Agency. 2010. Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean air Act (Technical Support Document). U.S. Environmental Protection Agency.

Reviewed 29 September 2010