Looking at a group of frogs found in biodiversity hotspots in Central and South America, scientists found links between higher temperatures and frog extinctions caused by a skin fungus. The infectious skin disease—a type of chytrid fungus (Batrachochytrium dendrobatidis)—is now found in frog populations around the world and is the main suspect in the rapid disappearance of amphibians.
Last year, the Global Amphibian Assessment, a survey of the planet's amphibian species, found that nearly a third (32%) of the world's 5743 known amphibian species are threatened and 129 species have gone extinct since 1980. Among the species to disappear is Costa Rica's Golden toad (Bufo periglenes) and the Gastric Brooding Frog (Rheobatrachus silus) of Queensland, Australia. Scientists believe there may be around 10,000 amphibian species on the planet, although this number is likely to be falling fast.
In linking climate change with frog extinction, an international team focused on the brightly colored harlequin frogs (Atelopus) which are critically endangered across their range—between the 1980s and 1990s, almost two-thirds of the 110 known harlequin frog species went extinct with the chytrid fungus the leading suspect.
Using records of sea-surface and air temperatures, the researchers discovered strong correlations between changes in climate and the last known sightings of the frogs. According to the scientists, the Earth's rising temperatures enhance cloud cover on tropical mountains, leading to cooler days and warmer nights, both of which favor the chytrid fungus which grows and reproduces best at temperatures between 63 to 77 degrees Fahrenheit (17 to 25 degrees Celsius).
The fungus kills frogs mostly in cool highlands or during winter, implying that low temperatures make it more deadly. Thus the disease flourishes in warm years and puts frogs living at mid-altitudes at greatest risk.
In coming years, further changes in climate change will likely produce conditions more favorable for the fungus and detrimental to frogs and other amphibians.
"Disease is the bullet that's killing the frogs," said scientists."But climate change is pulling the trigger. Global warming is wreaking havoc on amphibians, and soon will cause staggering losses of biodiversity," they said.
"The good news, if there is any, is the new findings will open up avenues of research that could provide scientists with the means to save the amphibians that still survive," said a zoologist who took part in the study. "If this cloud has any silver lining, that's it."
The new theory for the frogs' decline "leaps over a major roadblock in our understanding", said Sam Scheiner, program director for the National Science Foundation (NSF)'s ecology of infectious diseases program, which funded the research. "This study demonstrates the complex nature of global climate change, including how climate affects the spread of disease, and why these must be integrated if we are to understand and reduce threats to species extinctions."
Ecologists fear that the global decline of amphibians may have broader implications for the world's environment. Because amphibians have highly permeable skin and spend a portion of their life in water and on land, they are sensitive to environmental change and can act as the proverbial "canary in a coal mine", indicating the relative health of an ecosystem.

As they die, scientists are left wondering what plant or animal group is next.

Scheiner says global warming and the accompanying emergence of infectious diseases are a real and immediate threat to biodiversity and a growing challenge for humankind.
The disappearance of amphibians is troubling on other grounds as well. Many frogs and toads secrete toxic alkaloids to protect themselves from predators. These alkaloids have been found to have medical applications as pain killers. Thus the loss of each amphibian species eliminates the possibility of finding compounds with potential curative properties.
In September a group of conservation scientists proposed a $404 million effort to preserve declining global amphibian populations.
The strategy calls for funding from governments, private institutions and individual donors to finance long-term research, protect critical habitats, reduce the trade in amphibians for food and pets, and establish captive breeding programs. So far such programs have had mixed success.
The Kihansi Spray Toad, a small toad that is virtually extinct in the wild after its habitat was destroyed by a hydroelectric project in Tanzania, only exists today thanks to efforts by the Bronx Zoo of New York, the Detroit Zoo in Michigan, and the Toledo Zoo in Ohio.
Nevertheless, the toad's captive population has fluctuated dramatically in the past few years due to its biology (they breed in groups) and small size, and difficulties typically associated with captive amphibians.