NET BENEFIT: The positive effects of malaria control strategies such as bed netting could be 10 times larger than the negative ones of climate change, experts say. Image: UNITED STATES AGENCY FOR INTERNATIONAL DEVELOPMENT
While climate change may increase the occurrence of malaria, the effect can be almost completely offset by adopting control strategies such as bed netting, spraying and anti-malarial drugs, according to a paper published in the journal Nature.
"There are many claims about malaria increasing over the future climate change scenario," said Pete Gething, a co-author of the paper and a researcher at the Department of Zoology at the University of Oxford. "But it will be a small, negligible factor compared to present measures to counter it."
The potency of measures such as bed netting could be 10 times larger than the negative effects of climate change, said Gething.
Other researchers agreed in principle, but pointed out that the purpose of climate models is not to prove that the incidence of malaria will increase. Rather, the models are constructed to show that climate change and rising temperatures increase conditions that are conducive to the transmission of malaria.
"This is an attempt to counter something that isn't being said," said Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School. "You can't prove disease incidence."
It is a subtle point, but the incidence of a disease refers to its actual occurrence within a population. Climate models such as the one by the Intergovernmental Panel on Climate Change predict that with rising temperatures, the conditions that favor insect vectors such as the mosquito will allow disease transmission to become more prevalent.
Whether they will actually lead to a greater incidence of the disease will be complicated by factors including control measures, the availability of drugs, and even other indirect effects of climate change, such as population changes, migration and urbanization.
Critics say the conclusions are overstated
The current study measures disease incidence over the globe using two maps of malaria. The researchers compared a modern-day map from 2007 that shows the spread of infection by the malaria parasite Plasmodium falciparum throughout the world to a similar map constructed in 1900.
The 2007 map was a result of the Malaria Atlas Project, which aims to map the spatial spread of malaria. It showed that stable malaria covered 58 percent of the world's land surface at the beginning of the 20th century, and later decreased to 30 percent by 2007.
"During a century in which global temperature increases have been unequivocal, we have documented a marked, global decrease in the range and intensity of malaria transmission," states the paper.
Though the results sound intuitive, the correlation between climate change and the disease is simplistic, according to Kevin Lafferty, research ecologist at the U.S. Geological Survey.
"They have done a less convincing job matching malaria decline with climate change, besides noting that temperatures have increased over the past century," wrote Lafferty in an e-mail.
The researchers need to make more sophisticated connections between climate, malaria and the economics and control measures that will mitigate the disease, to get a full understanding of the issue, according to Lafferty.
"This is certainly difficult to do," he wrote. "It is useful that the authors repeat the point that projection of a global increase in malaria transmission have been overstated by some. But they overstate the overstatement."