Global warming sowing disease, extinctions, researchers say
Jan. 11, 2006
Special to World Science
Global warming has triggered epidemics that killed off dozens of amphibian species in tropical America, and is fomenting disease among other animals, researchers say.
Still with us, for now: The Panamanian golden frog, Atelopus Zeteki, one of the 110 or so species of harlequin frogs, a genus known from 11 tropical American countries. Unlike some harlequin frogs, this one isn't extinct yet, but its populations have dropped, researchers say. (Courtesy Forrest Brem).
It’s all part of an unpredictable spiral of warming-induced epidemics, they add—and there are signs that the phenomenon is starting to touch humans, who are far from immune to it.
A study published in the Jan. 12 issue of the research journal Nature reported that global climate change created favorable conditions for a deadly fungus in Central and South America. That led to widespread frog extinctions in mountainous areas.
Thousands of amphibian species have declined, and hundreds are on the brink of extinction or have already vanished, a group of 14 researchers said in the paper.
The fungus has killed off some two thirds of the 110 species of a colorful group known as harlequin frogs, they estimated.
That, they suggested, shows the climate change is killing off animals through more complex mechanisms than just higher temperatures—although studies have found that’s happening, too.
Scientists believe global warming is largely a result of industrially released gases that trap heat in the atmosphere. An international pact to curb these emissions, the Kyoto Protocol, has encountered resistance from the United States and other countries on grounds that the limits would harm their economies.
The authors of the Nature study, led by Alan Pounds of Costa Rica’s Monteverde Cloud Forest Preserve and Tropical Science Centre, said climate change is promoting infectious disease and destroying species.
In a commentary in the same issue of Nature, scientists said the amphibian crisis is just one example of unexpected, complex impacts from climate change that are becoming increasingly obvious.
The crisis is “an amphibian alarm call” and a harbinger of much worse disruption, said the researchers, Andrew R. Blaustein of Oregon State University in Corvallis, Ore. and Andy Dobson of Princeton University in Princeton, N.J.
Extinctions that once seemed puzzling are now believed to be linked to global warming, they added.
“The powerful synergy between pathogen transmission and climate change should give us cause for concern about human health in a warmer world,” said the university’s Andrew Blaustein in the Nature article. “As global change is occurring at an unprecedented pace, we should expect many other host taxa [organisms], from ants to zebras, to be confronted with similar challenges.”
Few of current studies consider how climate affects disease, said the researchers, and until this happens it will be hard to gauge global warming’s full effects.
Five years ago, in a study also published in Nature, scientists from the Oregon State University also found that warming and other climate changes in the Pacific Northwest of the United States were resulting in lowered water depths in mountain lakes, killing off many toads before birth.
“The climate change in the Arctic and sub-Arctic has modified the life cycle of the nematode parasites of musk oxen,” wrote Blaustein and Dobson. “These worms can now complete their life cycle in one year, instead of two, and their rising numbers are having a significant impact on musk oxen survival.”
A life cycle is the period between birth and reproduction, and when it’s shorter, an organism can spread more quickly, Blaustein said. “They can do more damage in much less time.”
Similarly, Blaustein said, the mountain pine beetle in parts of the western United States is completing its life cycle in one year, instead of two, leading to increasing problems with the fungus they carry.
Dengue fever, a deadly disease of humans, is increasing its range out of the tropics and is now found in parts of the southern United States, he added. Dengue fever is carried by mosquitoes who transmit any of four related dengue viruses. It was once called break-bone fever because it sometimes causes severe joint and muscle pain that feels like the bones are breaking. It sometimes kills younger victims.
Predicting how climate change will favor a certain pathogen or disease transmission is extremely hard, Blaustein and Dobson said: “We should expect the unexpected.”
* * *