Global warming alarmists frequently cite future increases in malaria deaths as one of the main reasons we need to stop burning fossil fuels. But Environment & Climate News readers know by now that
1) links between temperature and mosquito activity are very weak; 2) most of the warming is occurring in areas where there is no malaria; 3) rather than being confined to hot regions alone, malaria deaths historically have occurred at very high latitudes and during very cold periods; and 4) employing screens, or even mosquito nets, essentially eliminates the problem.
Nevertheless, a handful of boisterous malaria experts press onward with their case. Using the standard approach, they find locations where malaria occurs now, determine the range of conditions in which mosquitoes can survive, take the forecasts from a general circulation model (GCM) of future temperatures, determine where these mosquitoes will live in the future, and calculate the new at-risk population. The result, as you might guess, is always really bad news.
But never fear. There are many problems with this approach, several of which David Rogers and Sarah Randolph address in a recent paper in Science.
For one thing, Rogers and Randolph point out that a simplistic, temperature-based approach does not account for the multitude of climate factors that truly influence malaria transmission. As proof, they note that standard current models have significant area mismatches, or false-positives: locations that are predicted to have malaria but do not.
Using a more sophisticated model, Rogers and Randolph identified the suite of key climatic variables that describe the existing distribution of malaria. Then, using output from the United Kingdom’s Hadley Centre GCM for 2050, they predicted future malaria occurrence.
The results? Essentially no change! That’s right. Depending on which GCM warming scenario they used, malaria exposure is predicted to increase by only 0.83 percent, or to decrease by 0.92 percent, worldwide. Statistically speaking, these are both minuscule changes.
Malaria exposure is forecast to see this slight increase by 2050 in the southeastern United States and eastern Mexico, Turkey, Brazil, and China; and to undergo a slight decrease in Southeast Asia, India, northern Australia, the horn of Africa, and central South America.
The Rogers-Randolph result represents a major improvement over past methods. For instance, consider that simplistic, temperature-based methods forecast an expansion of malaria along the fringes of the Sahara Desert because of higher minimum temperatures. But when Rogers and Randolph include rainfall and other moisture variables, their more informed model predicts no expansion in this region.
Of course, Rogers and Randolph’s approach is nevertheless dependent upon the accuracy of the GCM used . . . and we all know how well they work.
And furthermore (bearing in mind that malaria incidence has less to do with climate than with human hygiene and other controls), by the year 2050, no doubt much more of the world will have the infrastructure in place to address whatever epidemiological problems may arise. As for the more politically responsive areas of the world, does anybody really believe that a malaria epidemic will hit Orlando, Florida, no matter how the climate changes?
In any event, this research is yet another addition to a fast-growing stack of evidence showing that climate change, where it does occur, will have no net negative impact on human health.
Robert E. Davis, Ph.D., is an associate professor of environmental science at the University of Virginia.
Rogers, D.J. and S.E. Randolph, 2000. The global spread of malaria in a future, warmer world, Science, 289, 1763-1766.