A study of the endangered Monteverde highlands of Costa Rica has revealed that rising temperatures are causing the moisture-laden mists to disappear. Already, 20 out of 50 species of frog and toad are believed to have perished.
Cloud forests are some of the world's most delicate ecosystems. They occur in the tropics when fine mists linger for weeks at a time over highland areas to create verdant hillsides rich in animals and plants.
Scientists believe that many species of amphibians and reptiles, unique to the area, are already extinct. One species endemic to Costa Rica, the golden toad, has not been seen for more than 10 years.
Alan Pounds, a researcher at the Monteverde Cloud Forest Preserve and Tropical Science Centre in Puntarenas, said the mysterious demise of so many species over such a short period of time can be linked with the decline in cloud cover at lower altitudes. The research team has also found that rising sea temperatures in the Pacific Ocean over the past 20 years appear to have pushed the mists in the Monteverde to higher-than- normal altitudes, starving the lower slopes of moisture.
Although a warmer ocean increases evaporation and causes more clouds to form, the temperature rise has meant that the clouds are more sparse over tropical mountain forests, Dr Pounds said.
The study found that the frequency of mists occurring at weather stations on the mountains over the past 20 years had declined, whereas temperature records for the same period showed the same amount of cloud cover - indicating it had not disappeared completely but formed instead on the higher slopes.
"Monteverde has become cloudier, yet drier. It's a paradox that can be explained by the clouds being higher," he said.
The heights at which the mists form fluctuate widely, but Dr Pounds says that rough estimates suggest that they may have risen by up to 200 metres - enough to destroy the delicately balanced habitats of cloud-forest animals.
Rising sea-surface temperatures, which are linked with global warming rather than with the El Nino ocean current, are probably behind the change, he added. "There's a real risk that if climate change continues on its present course we may indeed lose cloud forests. They are important areas for endemic species, because cloud forests contain species that exist no where else in the world."
Tim Halliday, a biologist at the Open University and director of the international task force set up to monitor the demise of amphibian species, said frogs and toads are particularly susceptible to outbreaks of disease - such as fungal attacks - when climate change forces them to group together near the dwindling water holes.
Since 1987, the Monteverde team has monitored the disappearance of 20 species of frogs and toads, including the red-eyed stream frog, rain frogs, treefrogs and the emerald glass frog.
However, other species of reptiles and birds have also been affected, Dr Halliday said. "Populations of forest lizards called anoles have disappeared in much the same way as amphibian populations.
"Because the fungi which infect the moist skins of frogs, toads and salamanders are unlikely to attack reptiles, climate change, rather than a particular disease organism, may be the common denominator in the declines," he said.