Is Global Warming Nurturing Parasites?
Plant, Animal Diseases Flourish in Changed Climates, Study Says
Listen to Christopher Joyce's report.
View a photo gallery of flora and fauna affected by global warming.
June 20, 2002 -- Elephantiasis, dengue fever -- Americans haven't worried about those tropic-region diseases because they couldn't survive in more temperate climates. But that could change soon, according to a group of scientists who've examined animal and plant diseases worldwide. They contend that global warming may be making the world a better place -- for parasites. For All Things Considered, NPR's Christopher Joyce reports on a new study from Science Magazine.
In outbreaks of disease such as malaria or West Nile virus, "usually people are the problem," says Joyce. "They ship agricultural products around the world, or war puts refugees and disease on the highways of the world."
But animals and plants tend not to do these things -- and yet they seem to be getting sicker, says Richard Ostfeld of the Institute of Ecosystem Studies in New York. "What our studies found was other diseases that don't strike humans -- ones that strike things like Hawaiian birds, marine corals, trees, crop plants and things like that -- are also expanding," Ostfeld says.
Take Hawaiian birds, for example. They get a form of malaria from mosquitoes. At low altitudes the disease is everywhere, but up until now the mountains were too cold for the mosquitoes. Not any more. Climate warming has pushed warmer air high up, and mountain birds are suffering.
Ostfeld's fellow researcher, "disease ecologist" Andrew Dobson, says he has wondered for years whether a warming climate is increasing disease outbreaks. Now he thinks he has an answer: "Changes in climate are beginning to have interesting and potentially dramatic effects on the way infectious diseases affect wildlife." In temperate climates, for example, cold winters are a natural way to kill off a lot of diseases carried by insects or ticks. But warmer winters mean more will survive; and the heat also puts extra stress on plants and animals, and makes it harder for them to fight off disease.
Such effects of global warming have long been predicted, says Joyce: "What's been lacking is evidence that it's actually happening." But after examining research around the world, Dobson, Ostfeld and their co-authors conclude in Science Magazine that the evidence is getting stronger.
Other examples the researchers cite: Warmer temperatures seem to have worsened several types of fungus that attack oak, elm and beech trees. Livestock diseases carried by insects in Africa have recently spread to new areas farther from the equator. And unusually warm water from the El Nino event in 1998 caused coral to sicken and die.
The researchers acknowledge that what they've got is "still mostly anecdotes," Joyce says. "But they say the weight of those anecdotes is beginning to make climate change look pretty guilty."