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Climate change can threaten entire species by altering the way disease spreads, according to research on frogs that is among the first to link global warming, disease and extinction.

"Disease is the bullet killing frogs, but climate change is pulling the trigger," says Alan Pounds of the Monteverde Cloud Forest Preserve in Costa Rica, lead author of the study in this week's Nature (12 January).

Scientists have struggled to explain why amphibians are disappearing from seemingly undisturbed areas, especially on mountains, in many parts of the world.

For example, nearly two-thirds of the 110 species of harlequin frog in Central and South America have disappeared since 1980. The fact that adult frogs have been dying in large numbers suggests that disease may be to blame.

Now, Pounds and colleagues have shown that a fungus that lives on frog skin together with changes in local weather conditions linked to global climate change are behind the extinctions.

Earlier attempts by Pounds to link the frog extinctions to the fungus were compounded by a paradox: climate change seemed to be warming the region, yet this type of fungus was known to be more lethal to frogs in cooler climes.

The latest study reveals that, in fact, both extreme hot and cold temperatures stop the fungus from killing frogs.

Rising temperatures, say the researchers, are creating more clouds over parts of Latin America, which is reducing temperatures by day and making nights warmer.


The Central American
harlequin frog

"This is moderating the extremes that can hold back the fungus," explains Pounds.

The study's implications reach beyond the amphibian realm.

Researchers have long suggested that changing climates will affect many human diseases, including dengue fever, malaria and cholera. But the numerous factors that contribute to causing an epidemic of these diseases makes this a difficult theory to explore.

"This new study is a breakthrough, and the powerful synergy between pathogen transmission and climate change should give us cause for concern about human health in a warmer world," write conservation biologists Andrew Blaustein and Andy Dobson, in an accompanying commentary in Nature.

Link to full paper in Nature

Reference: Nature 439, 161 (2006)

Link to full commentary by Blaustein in Nature