Climate Change Brings Risk of More Extinctions
Monday, September 17, 2007
BLACKWATER NATIONAL WILDLIFE REFUGE, Md. -- Third in a monthly series
What has gone missing here is almost as spectacular as the 8,000 acres of swampy wilderness that remain. And that makes it Chesapeake Bay's best place to watch climate change in action.
Visitors can see ospreys gliding overhead, egrets wading in the channels and Delmarva fox squirrels making their unhurried commutes between pine trees.
But then the road turns a corner, and Blackwater's marsh yields to a vast expanse of open water. This is what's missing: There used to be thousands more acres of wetland here, providing crucial habitat for creatures including blue crabs and blue herons. But, thanks in part to rising sea levels, it has drowned and become a large, salty lake. "If people want to see the effects" of Earth's increasing temperature, refuge biologist Roger Stone said, "it's happening here first."
But not just here. Around the world, scientists have found that climate change is altering natural ecosystems, making profound changes in the ways that animals live, migrate, eat and grow. Some species have benefited from the shift. Others have been left disastrously out of sync with their food supply. Two are known to have simply disappeared.
If warming continues as predicted, scientists say, 20 percent or more of the planet's plant and animal species could be at increased risk of extinction. But, as the shrinking habitat at Blackwater shows, the bad news isn't all in the out years: Some changes have already begun. "This is actually something we see from pole to pole, and from sea level to the highest mountains in the world," said Lara Hansen, chief climate change scientist at the World Wildlife Fund, a private research and advocacy group. "It is not something we're going to see in the future. It's something we see right now."
The temperature increase behind these changes sounds slight. The world has been getting warmer by 0.2 degrees Fahrenheit every decade, a U.N. panel found this year, in part because of carbon dioxide and other human-generated gases that trap heat in Earth's atmosphere.
By nature's clock, the warming has come in an instant. The mechanisms that helped animals adapt during previous warming spells -- evolution or long-range migration -- often aren't able to keep up. Scientists say that effects are beginning to show from the Arctic to the Appalachian Mountains. One study, which examined 1,598 plant and animal species, found that nearly 60 percent appeared to have changed in some way.
"Even when animals don't go extinct, we're affecting them. They're going to be different than they were before," said David Skelly, a Yale University professor who has tracked frogs' ability to react to increasing warmth. "The fact that we're doing a giant evolutionary experiment should not be comforting," he said.
Some of the best-known changes are happening near the poles, where the air and the water are warming especially quickly. As they do, sea ice is receding. For some animals, this has meant literally the loss of the ground beneath their feet.
Polar bears, for instance, spend much of their life on the Arctic ice and use it as a hunting ground for seals. When ice on Canada's western Hudson Bay began to break up earlier -- three weeks earlier in 2004 than in 1974 -- the effect was devastating. The bear population fell by 21 percent in 17 years. Shrinking ice has also been blamed for cannibalism among polar bears in the waters off Alaska, something scientists had not seen before 2004. This month, a U.S. Geological Survey report predicted that two-thirds of the world's polar bears could die out in 50 years.
Walruses, too, rely on the ice; mothers stash their calves on it, then dive down to feed on the ocean floor. When ice recedes from prime feeding areas, mothers and calves can get separated.