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Global warming has triggered the decline of hundreds of species of frogs and toads by helping a deadly skin infection to spread across the world.

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 decline of the 6,000 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 called Batrachochytrium dendrobatidis with a rise in tropical temperatures associated with global warming. The scientists believe 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 the journal Nature, said the analysis firmly linked climate change with the demise of many frogs and toads. "With this increase in temperature, the fungus has been able to increase its niche and wipe out large populations of amphibians," he said. The rapid loss of amphibians - frogs, toads, newts and salamanders - has led to about one- third of them, some 1,856 species, being classified as threatened. Hundreds more face extinction.

Scientists believe the chytrid fungus is behind the disappearance of the golden toad of Costa Rica and at least 67 per cent of the 110 species of brightly coloured harlequin frogs that have vanished from the tropical forests of South and Central America over the past 17 years.

Alan Pounds of the Monteverde Cloud Forest Preserve in Costa Rica, and the lead author of the study, said the higher average air temperatures in the region were 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," Professor Pounds said.

He said that rising temperatures enhanced cloud cover over tropical mountains leading to cooler days and warmer nights, both of which favoured the growth of the fungus. The discovery helps to overcome a paradox that puzzled scientists because warmer air temperatures should not in fact favour the spread of the fungus, which thrives best in cooler, damper conditions.

It was known that the fungus killed frogs mostly in cool highland regions, implying that low temperatures made it more deadly. The study found that the chytrid fungus was vulnerable to extremes in temperature and anything that moderated these extremes could unleash it.