Study: Global warming killing frog species

Rising temperatures are responsible for pushing dozens of frog species to extinction in the past three decades, according to new findings being reported today by a team of Latin American and U.S. scientists.

The study, published in the journal Nature, provides concrete evidence that climate change has already contributed to wiping out species and could spur more extinctions and the spread of disease worldwide. It also helps solve the mystery of why amphibians across the globe have been vanishing from their usual habitats over the past quarter-century: As many as 112 species have disappeared since 1980.

Scientists have speculated that rising temperatures and changing weather patterns could endanger the survival of many species, but the new study documents for the first time a direct correlation between global warming and the disappearance of roughly 65 amphibian species in Central and South America.

The fate of amphibians, whose permeable skin makes them sensitive to environmental changes, is seen by scientists as a possible harbinger of global warming's effects. Rising temperatures are threatening the survival of plants and animals worldwide, from coral reefs in the Caribbean that serve as critical fish nurseries to South African rhododendrons.

J. Alan Pounds, resident scientist at the Tropical Science Center's Monteverde Cloud Forest Preserve in Costa Rica and the study's lead author, worked with 13 other researchers to pin down the link between rising temperatures in the tropics and the spread of the deadly chytrid fungus, which has wiped out dozens of species of harlequin frogs in recent years.

"Disease is the bullet killing frogs, but climate change is pulling the trigger," Pounds said. "Global warming is wreaking havoc on amphibians and will cause staggering losses of biodiversity if we don't do something first."

The paper helps explain how global warming has allowed the chytrid fungus, which kills frogs by attacking their skin and teeth as well as by releasing a toxin, to thrive in Costa Rica and neighboring countries. The higher temperatures result in more water vapor in the air, which in turn forms a cloud cover that leads to cooler days and warmer nights. These conditions favor the fungus, which grows and reproduces best at temperatures between 63 and 77 degrees Fahrenheit.

At least 110 species of the vibrantly colored amphibians once lived near streams in the Central and South American tropics, but about two-thirds disappeared in the 1980s and '90s. While researchers had previously identified the fungus as a major reason for the frogs' demise, they have been trying to determine why the disease has taken such a major toll in recent years.

Looking at more than 65 harlequin frog species that had vanished, researchers found that 80 percent of the time there was a correlation between higher temperatures and the species' disappearance.

After a warm peak in 1987, for example, five species died off.

"There's a coherent pattern of disappearances, all the way from Costa Rica to Peru," Pounds said. "Here's a case where we can show that global warming is affecting outbreaks of this disease."

Amphibians are experiencing a precipitous decline in Africa, Asia and North America, according to a comprehensive 2004 survey, which cited climate change as well as deforestation, pollution and habitat loss as key factors.