Is Global Warming Leading to Extinction?

The mist's cooling moisture is vital to thousands of local animal species, like this captive glass frog, whose pumping heart you can see through its skin. Glass frogs also sing.

"This used to be a great place for listening to glass frogs at night," says Pounds. "You could hear them over the roar of the waterfall"

But not any longer. Since the late 1980s, this Cloud Forest preserve has been under a complicated attack from global warming. "Birds, reptiles, mammals… a variety of species have been affected," says Pounds.

Where Have All the Clouds Gone?

We first met American scientist Alan Pounds here 11 years ago when he was trying to figure out why Monteverde's famous Golden Toad and Harlequin frog had vanished.

He had begun to suspect something in the weather. And now, still living in his tiny house in the forest and crunching hard data that he and others have collected, he's got some answers.

After years of monitoring animal populations, tracking fluctuations in the mist and working with climatologists, he found the warmer temperatures are making the clouds form higher up. The clouds' base had lifted, making "them less effective in delivering moisture to the forest," says Pounds.

The normal brief dry spells, have been getting longer. And plotting the length of dry spells each year, parallel to the number of species that disappeared each year, he found they matched exactly.

"The patterns suggest quite strongly that the changes are climate-related," says Pounds.

Invasion of the Aggressors

The warmer temperatures attack different species differently. And scientists such as Pounds can't always tell exactly how it attacks any one species. Monteverde's missing frogs may well have succumbed to a fungus that clogs their permeable skin.

"We think changing climate is affecting the probability of outbreaks or helping certain diseases spread over the landscape, loading the dice for epidemic outbreaks," says Pounds.

But animals that don't get that disease -- birds, insects and reptiles -- also disappeared in the drier years. The reason might be because as the clouds move up the mountain, so do other more aggressive species.

Pounds showed us lizards and birds such as the long-beaked toucan.

"This is a toucan from further down the mountain but it's started moving up into the cloud forest," says Pounds. Its big beak is adapted to reach into nests of other species and steal eggs.

"There's a lizard," he showed us. "This is an example of a species that has moved up the mountain. It's increasing in abundance at this altitude and the species that used to be very abundant here? Now, we don't see them at all."

No Refuge at the Mountain Top

Such changes are occurring atop other tropical mountains also bathed in mist -- in Madagascar. Expeditions led by scientist Chris Raxworthy of the American Museum of Natural History, also find a number of animal species are scrambling upslope in tandem with the rising temperatures.

But even at the top of the mountain, there may be no safety. Scientists there find that three species of frogs, last seen in 1993, are now missing.

"All three of them were found at the very top of the mountain," says Raxworthy. "Perhaps they've gone extinct… when species get to the top of a mountain they have nowhere to migrate to, they have no option but to go extinct."

Species have started "falling off mountaintops," as scientists put it, in many countries.

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