Frogs heading dinosaur's way

The decline in amphibians has left about a third officially classified as threatened

Global warming has triggered the extinction of hundreds of species of frogs and toads.

Scientists believe they have found the first clear proof that global warming has caused outbreaks of an infectious disease that is wiping out entire populations of amphibians.

The dramatic demise of the 6000 species of amphibians was first identified in 1990 and one theory for the loss was the spread of a devastating skin infection caused by a fungus.

A study by an international team of researchers has now linked the spread of a species of chytrid fungus with a rise in tropical temperatures associated with global warming.

The scientists believe that the average temperatures of many tropical highland regions, which are rich in endemic species of frogs and toads, have shifted to become perfect for the growth of the fungus.

Arturo Sanchez-Azofeifa of the University of Alberta in Canada, one of the authors of the study published in Nature this week, said that the analysis firmly links climate change with the rapid demise of many frogs and toads.

"There is absolutely a linkage between global warming and this disease, they go hand in hand," Professor Sanchez-Azofeifa said. "With this increase in temperature, the fungus has been able to increase its niche and wipe out large populations of amphibians in the Americas."

The dramatic loss of amphibians - frogs, toads, newts and salamanders - has led to about a third of them, some 1856 species, being officially classified as threatened. Hundreds more are on the brink of extinction.

Alan Pounds of the Monteverde Cloud Forest Preserve in Costa Rica and the lead author of the Nature study, said that the average air temperatures in the region are responsible for the spread of the fungus.

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

The study found that between 1975 and 2000, average air temperatures for the tropics increased by 0.18C per decade - triple the average rate of warming for the 20th century. Most "extinctions" - when the species was last sighted - occurred in unusually warm years.

The likelihood of this association being chance was less than one in a thousand.

Professor Pounds said that rising temperatures enhance cloud cover over tropical mountains leading to cooler days and warmer nights, both of which favour the growth of the fungus.

The discovery helps to overcome a paradox that puzzled scientists for warmer air temperatures should not favour the spread of the fungus, which thrives best in cooler, damper conditions. It was known that the fungus kills frogs mostly in cool highland regions or during winter months, implying that low temperatures make it more deadly. The study, however, found that the fungus is vulnerable to extremes in temperature and anything that moderates these extremes - such as more frequent mists and clouds in warmer weather - can unleash it.

"This new study ... should give us cause for concern about human health in a warmer world," said Professor Andrew Blaustein, a zoologist at Oregon State University.

"As global change is occurring at an unprecedented pace, we should expect many other [animals] from ants to zebras to be confronted with similar challenges."

- INDEPENDENT