Quotes of the Day

The threats to wildlife on the African island of Madagascar are manifold: rampant deforestation that has stripped most of the island of its original forest cover, leaving a wasteland; a human population that is growing at 3% a year, straining natural resources and hunting animals for food, especially Madagascar's emblematic lemurs; extractive industry, including a nickel mine not far from a national park that could become the world's biggest.

There's another danger that's invisible, but may be more dangerous than the others put together: climate change. Global warming will do to wildlife what it may do to humans. As the climate changes, animals may be forced to move out of the habitats they're accustomed to — like human refugees. "Global warming is something that all conservationists are worried about," says Russell Mittermeier, the president of Conservation International. "It has the possibility to undo a lot of the work we've done." (Hear Mittermeier discuss the impact that climate change on conservation, and the situation in Madagascar, on this week's Greencast.)

While the impact of climate change on human populations is likely to be dire, we're pretty good at adapting to change overall. Animals, however, are not. When their habitats change irrevocably — when the rain forest dries up or cool mountains in tropical zones heat up — animals may simply go extinct. A recent study in Science demonstrates how that can happen. Robert Colwell, an evolutionary biologist at the University of Connecticut, analyzed data from nearly 2,000 species of plants, insects and fungi in the tropics, where organisms often lack the ability to escape warming temperatures by going north or south; instead, they have to go up in elevation to find cooler temperatures. Colwell found that as populations in lowland areas move up, they tend not to be replaced. That means that we may see a reduction in overall biodiversity and what scientists call "species richness." Meanwhile, species that already live at the highest elevations have no place to go, except perhaps to extinction. Case in point: the Golden Toad, which lived in the high-altitude cloud forests of Costa Rica and suddenly went extinct. Its disappearance may be due in part to warming, which made its habitat unlivable.

The toad may be the first animal whose extinction scientists will link to global warming, but it certainly won't be the last. Last year, the U.N.'s Intergovernmental Panel on Climate Change estimated that if global temperatures increase more than two to three degrees F above current levels — which seems quite possible, given current trends in carbon emissions — up to one-third of the species on Earth could be at risk for extinction. "We're already seeing nature react badly to climate change," says Larry Schweiger, the president of the National Wildlife Federation. "We're changing the rules of the game."

For one thing, the grand design of conservationism is to create reserves, protected areas like national parks where wildlife can live free from the impact of human populations. That strategy has been overwhelmingly successful, but conservationists now fear that global warming could make those reserves meaningless, if animals that are accustomed to a different climate can't survive in them. "We're used to focusing on protecting real estate," says Schweiger. "Now we have to be able to make sure animals can move to safe areas."

First, conservationists say, we need to do everything we can to slow carbon emissions and reduce the impact of climate change. "That's priority number one," says Mittermeier. But some degree of warming is inevitable, so conservationists have to prepare. That means creating not just reserves, but safe nature corridors that would allow wildlife to migrate in the face of rising temperatures. Another method is to try to connect existing reserves through reforestation — a technique already underway in Madagascar, where the government is looking to vastly increase the total amount of protected land. What's certain is that we need to act. If we don't, says Schweiger, "Climate change could undermine the conservation work of whole generations."

• Bryan Walsh