Bob Holmes, New Scientist 11 Apr 09;
MUD-SLINGING has broken out among ecologists over a study suggesting that climate change might not spread tropical diseases far and wide after all. When the paper triggered an uproar, editors at the journal Ecology decided to publish not one but six responses alongside the original research. The collection appears in the April issue.
Many disease researchers have warned that rising global temperatures could lead to more disease, for example by allowing tropical diseases to expand their ranges into what are now temperate regions. This is a particular fear for insect-borne diseases such as malaria and sleeping sickness.
But the reality is more complex, argues Kevin Lafferty, a disease ecologist at the US Geological Survey's Western Ecological Research Center in Santa Barbara, California. He argues that a warming climate could favour some diseases in certain regions while inhibiting them in others.
Lafferty does not deny that climate change might allow malarial mosquitoes to spread to new areas. However, he believes that hotter and drier conditions may also eliminate mosquitoes from areas where they currently thrive, such as the Sahel region in Africa. If this were the case, he says, there would be little if any net increase in the risk of disease.
In addition, many temperate regions such as southern Europe or the southern US have good sanitation and insect control programmes which, Lafferty says, would prevent diseases from becoming prevalent even if climatic conditions were suitable.
Finally, he argues, climate change could wipe many species off the planet. Infectious pathogens depend on their hosts for survival so they too may become endangered - especially if, like malaria, they rely on more than one host (Ecology, vol 90, p 888).
Lafferty's paper caused such a furore among its reviewers that the editor handling it, Ken Wilson of Lancaster University in the UK, commissioned a series of responses arguing both sides of the debate to publish alongside it.
"I disagree with the whole line of reasoning," says Mercedes Pascual of the University of Michigan in Ann Arbor. She points out that there are large human populations in the east African highlands, just outside of the existing range of malarial mosquitoes, and as temperatures rise, the mosquitoes will reach these areas. This will more than offset any benefits from decreased risk elsewhere, she says (Ecology, vol 90, p 906).
Richard Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, New York, says that while better health infrastructure in developed nations "might be heartening to some, it is far from universal". For instance, several ecologists point out that there is evidence climate change is already increasing the incidence of malaria in the highlands of Ethiopia, where poor health infrastructure will harm any response.
Climate change is probably also causing an increase in non-human diseases. Drew Harvell, an ecologist at Cornell University in Ithaca, New York, says winter warming in the Caribbean is leading to increased rates of disease in corals (Ecology, vol 90, p 912).
Most of the ecologists do, however, seem to agree on one point: predicting where a disease is going to go next involves far more than just climate. No matter how the debate is resolved, they all agree that health concerns should continue to play a critical role in climate policy, and the debate shouldn't be regarded as weakening the case for action on global warming.
