Bad Air Gets Worse


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Malaria kills about 1 to 2 million people a year worldwide. About 90 percent of new cases occur in Africa and Southeast Asia. Although the disease is now rare in developed countries, that could change with global warming, researchers in Italy warn. As soon as 50 years from now, they say, malaria could spread to parts of the world that are now too cold to support the life cycle of the mosquitoes and their parasites that transmit the disease.

Some 50 to 60 different mosquito species of the Anopheles genus harbor the four species of parasite--a single-celled protozoan called a plasmodium--that cause malaria. The most dangerous of the four dies at temperatures below about 66 degrees Fahrenheit. In temperate countries, cool weather, the draining of swamps, and the use of pesticides have made malaria outbreaks rare. Unfortunately, that could change with global warming, says environmental physicist Philippe Martin.

People think if it’s a bit hotter, then we’ll just put a little bit more power in our air-conditioning, says Martin. But the implications of global warming, he says, can be far more insidious than higher electricity bills. He and his colleagues at the Joint Research Center of the European Commission in Italy collected data from five meteorological models made by research labs and universities around the world. Each model projected how Earth’s climate would change under the assumption that the current atmospheric carbon dioxide level would double in the next 50 to 100 years.

Using these models, Martin and his colleagues predict a 7 to 28 percent increase in the territory where malaria could occur. Although the disease-bearing mosquitoes can exist in many temperate areas now, public health and mosquito eradication programs now keep malaria in check. The existing infrastructure may be overwhelmed if conditions are really improved for the transmission of the disease, says Martin.

Most of the new malaria territory falls in the Northern Hemisphere and Australia. In parts of Asia and Africa, the researchers predict, warmer weather will occasionally dry up the stagnant pools in which mosquitoes breed. But far from being good news, they say, this change would be very bad: it means that people in those areas will no longer be exposed to malaria year-round, will have less chance to build up resistance, and will thus become vulnerable to far more deadly seasonal epidemics.

Like all climate-related predictions, the prediction of a malaria expansion is shrouded in uncertainties. For instance, it’s possible we won’t keep emitting carbon dioxide at current rates. If we quit dumping carbon dioxide into the atmosphere today, then this will not happen, says Martin. I would be happy if I were entirely wrong, because it would mean that we’ve done something about these problems.

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