When the summer sea ice goes, the Arctic will lose the ivory gull, Pacific walrus, ringed seal, hooded seal, narwhal and polar bear—all animals that rely on the ice for foraging, reproduction or as refuge from predators. And the sea ice is going, faster and faster: In the past 30 years, minimum sea ice cover in the Arctic Ocean has declined by 45,000 square kilometers annually*—an area twice the size of New Jersey is lost each year.

"Sea ice is like rainforest in the tropics. There are species that can't live without it," says ecologist Eric Post of The Pennsylvania State University, lead author of a paper in the September 11 Science that lays out a broad review of climate change's impact on the Arctic. "It's melting earlier, freezing up later, the contiguous extent is diminishing, and it's happening faster than anyone expected it to happen 10 years ago."

As a wrap-up of ecological studies conducted during the Fourth International Polar Year, Post and a slew of colleagues surveyed the state of the Arctic and found it to be not good, thanks to climate change. "We looked at plants and animals: vascular and nonvascular plants, migratory and nonmigratory animals, vertebrates and invertebrates, saltwater and freshwater, on the land or in the air—everything is changing," Post says. "It doesn't really matter where you look in the Arctic. Things are changing fast."

Rapid change is coming even for animals once thought to be relatively immune, such as caribou. Whereas the nonmigratory population of the animals on the Norwegian Svalbard Islands is burgeoning thanks to more winter snowmelt exposing a greater abundance of plant life for foraging, caribou in other parts of the Arctic are suffering. In spring, plants are blooming earlier in the year thanks to warmer early spring temperatures, but caribou are still calving at the same time, meaning calves are born after most of the food is available, and therefore fewer of them survive.

"I had no idea caribou could be on the brink of collapse. They seemed to have all the right traits to adapt," Post says. "Now they're of critical concern."

Particularly to the peoples of the Arctic who, in many cases, rely on hunting caribou or other animals to survive. "If you talk to the Inuit people in Greenland, they are suffering consequences for something they haven't contributed to themselves," Post notes. "We're taking away elements of a lifestyle that has worked for them for thousands of years. If somebody was doing that to us, don't you think we'd be upset?"

But the list of effects do not stop with the loss of a way of life and sea ice or the mismatch between spring blooms and caribou birthing: red foxes are replacing Arctic foxes farther and farther north; snow cover is diminishing; early spring rains now wash away seal dens, exposing pups; unusually warm periods in winter kill off Arctic plants and they do not rebound the following summer; and lemming and vole populations have crashed and remained at low levels for nearly a decade without recovering, among others. "There's been such a decline in snow cover that it affects [rodent] survival," Post says. "It means that species like snowy owls and Arctic foxes that are dependent on finding rodents will also suffer."

This is all happening with an increasing temperature of just one degree Celsius over the past century. In the next 100 years, the Arctic might warm as much as 6 degrees Celsius according to the United Nations Intergovernmental Panel on Climate Change. "If it were to get to three degrees [Celsius] warmer on average, the Arctic would be a thing of the past," Post says. "Polar bears, long winters of snow, sea ice cover—it wouldn't be the case anymore."

Instead the Arctic might become more like the boreal forests of Alaska, Canada, Scandinavia and Siberia—vast stands of spruce trees that do not support the unique Arctic flora and fauna.

The problem confronting Arctic species is not the warming itself, of course; there have been similar episodes in Earth's history, such as the warming during the transition from the Pleistocene to the Holocene epochs. It is the speed with which the greenhouse gases from fossil fuel burning are warming the globe. "The rate of change is so fast now," Post says. "It's about whether it's getting warmer over several decades or one decade. For a long-lived species there's no chance to keep up, no chance for evolution to keep up."

For his part, Post is hoping that the world will begin to treat Arctic biodiversity as worthy of conservation, more like tropical biodiversity, for example. After all, the Arctic is actually abundant with unique species and ecosystems, not a lifeless, white wasteland.

Post's report is not all bad news: Arctic warming has begun to promote the spread of trees and shrubs farther north, and the growth of these plants can lock up more carbon dioxide as they flourish.

Unfortunately, the warmth is also permitting the northward march of insect pests like the winter moth, which defoliates trees and shrubs and reduces the overall carbon sequestration. Plus, the advance of shrubs is affecting ecosystems, promoting more microbial activity in the soil and, ultimately, the release of methane—another greenhouse gas that traps 25 times as much heat as carbon dioxide over 100 years in the atmosphere.

In other words, warmth—and big changes for the Arctic—will keep coming. "Even if we restrict carbon emissions, it will get warmer," Post says, thanks to the greenhouse gases already in the atmosphere and feedback effects like the loss of sunlight-reflecting sea ice and snow cover. "That doesn't mean we shouldn't curb emissions. It's a matter of damage control.... We might be losing the Arctic as we know it but we need to do everything we can to make sure the problem doesn't spread."

* (9/10/09): This sentence has been changed to clarify that the sea ice loss figure is an annual number.