By Doug Struck
Washington Post Staff Writer
Monday, October 22, 2007; A10

Fourth in a monthly series

For scientists, global warming is a disaster movie, its opening scenes set at the poles of Earth. The epic already has started. And it's not fiction.

The scenes are playing, at the start, in slow motion: The relentless grip of the Arctic Ocean that defied man for centuries is melting away. The sea ice reaches only half as far as it did 50 years ago. In the summer of 2006, it shrank to a record low; this summer the ice pulled back even more, by an area nearly the size of Alaska. Where explorer Robert Peary just 102 years ago saw "a great white disk stretching away apparently infinitely" from Ellesmere Island, there is often nothing now but open water. Glaciers race into the sea from the island of Greenland, beginning an inevitable rise in the oceans.

Animals are on the move. Polar bears, kings of the Arctic, now search for ice on which to hunt and bear young. Seals, walrus and fish adapted to the cold are retreating north. New species -- salmon, crabs, even crows -- are coming from the south. The Inuit, who have lived on the frozen land for millennia, are seeing their houses sink into once-frozen mud, and their hunting trails on the ice are pocked with sinkholes.

"It affects everyone," said Carin Ashjian, a Woods Hole Oceanographic Institute scientist who spent early September with native Inupiats in Barrow, the northernmost town of Alaska. "The only ice I saw this year was in my cup at the cafeteria."

At the South Pole, ancient ice shelves have abruptly crumbled. The air over the western Antarctic peninsula has warmed by nearly 6 degrees since 1950. The sea there is heating as well, further melting edges of the ice cap. Green grass and beech trees are taking root on the ice fringes.

Antarctica's signature Adelie penguins are moving inland, seeking the cold of their ancestors, replaced by chinstrap and Gentoo penguins, which prefer open water. Krill, the massive smorgasbord for a food chain reaching to the whales, are disappearing from traditional spawning grounds.

"We've seen quite big changes in the living environment," John King, a lead researcher for the British Antarctic Survey, said from Cambridge, England.

The scenario is not new. What is most alarming to the scientists is the speed at which it is unfolding. A decade ago, melting at the poles was predicted to play out over 100 years. Instead, it is happening on a scale scientists describe as overnight.

When the Larsen B, an Antarctic ice shelf the size of Rhode Island, collapsed in 2002, "it was a big glaring clue that something not natural was happening," said Hugh Ducklow, director of ecosystems for MBL Laboratories in Woods Hole, Mass. "The geological evidence suggested that was stable for at least 10,000 years, back to the last ice age. And it literally disintegrated in three weeks."

The scientists say the coming scenes in the movie, as described by the historic melding of research assembled by the Intergovernmental Panel on Climate Change, will be even more disturbing:

As the air warms over Canada, Alaska and Siberia, the melting permafrost releases millions of tons of trapped carbon and methane, further accelerating the encroaching disaster. Greenland's moving glaciers pick up speed, likely bringing in this century the first three feet of a possible 23-foot rise of the seas that would ultimately inundate New York City and South Florida and drive millions of people from low-lying areas of Asia.

The ice shelves collapsing in western Antarctica bring glacier melting there, pouring as much water into the sea as Greenland. Eventually, the giant frozen continent of eastern Antarctica, so far insulated from the rest of the warming planet, may begin to melt. The thermohaline ocean circulation pattern begins to slow.

"I just don't see a happy ending for this," said Ted Scanbos, who studies the polar ice at the National Snow and Ice Data Center at the University of Colorado.

Most scientists say the changes anticipated at the poles in the next 30 to 40 years are inevitable, and averting more severe effects will take a drastic reduction in emissions of greenhouse gases. Some have advanced controversial ideas to exploit the polar systems. At least three companies have plans to "fertilize" the Southern Ocean with iron try to soak more carbon dioxide out of the air.

"We are just leveraging a natural process," said Dan Whaley, founder of Climos, a San Francisco company. Other scientists gathered recently at the Woods Hole Oceanographic Institute were skeptical of the idea. "There will be scientific consequences we cannot predict," warned John Cullen, an oceanographer at Dalhousie University in Halifax.

The polar regions have been regularly described as the canaries in the coal mine of global warming: remote bellwethers that could give mankind a heads-up when important changes are coming.

Some even see positive opportunities in the warming. The legendary Northwest Passage, a sea route from the Atlantic to the Pacific above North America, is now mostly ice-free in the summer. That opens up tempting commercial possibilities for shippers and for drillers seeking vast oil and gas fields under the Arctic Ocean. Arctic nations including Canada, Norway, the United States and Russia are engaged in an increasingly urgent race to map out the ocean floor and stake claims on undersea resources.

But it turns out that the polar regions are far more than simple alarms. What happens at the poles will -- and is -- affecting the rest of the world.

Consider the permafrost. The vast Arctic region in the north encompasses land on three continents that has been deeply frozen since the last ice age. A thin layer thaws each summer. By mid-century, half of it will thaw to 10 feet, according to computer models of the National Center for Atmospheric Research in Boulder, and long-trapped greenhouse gases will be released.

Already, the melting in Siberia is releasing methane, a potent greenhouse gas, that had been buried for 40,000 years, feeding a cycle of more warming and more melting.

"That's a serious runaway," Scanbos said. "A catastrophe lays buried under the permafrost."

Or consider the ocean currents. The weather in the Northern Hemisphere is controlled by the temperature of currents that circulate on a giant treadmill, in which water cooled at the icy poles sinks to the bottom, and moves slowly toward the equator, where it heats and rises to flow northward again, mixing the seas. That is why Europe's climate is relatively moderate.

As the Arctic ice melts and ice shelves collapse in the Southern Ocean, vast areas of open water are exposed. The water absorbs heat from the sun that until now was reflected by the ice. As that heat warms the seas, the treadmill is expected to slow, the IPCC has reported. In the worst case, it could stop. The previous time that happened, 15,000 years ago, the Northern Hemisphere was plunged into a brief and brutal ice age, apparently within decades.

"It's like having a pool of warm water sitting in the middle of what is supposed to be the air conditioner of the north," Scanbos said. "And it will be within our lives, not our grandchildren's."

The northern Arctic is changing first, and most noticeably. But the changes there are likely to be followed by a "one-plus-two-plus-three punch" in the southern polar region, said Ellen Mosley-Thompson, at the Byrd Polar Research Center at Ohio State University. She has been drilling and measuring ice in polar regions and mountain glaciers for 25 years, and has lived in frigid tents and battled brutal weather for weeks at a time to get ice core samples.

The Antarctic has sent complicated signals, she said. The interior is "a monstrously large ice sheet that creates its own microclimate." Winds circling Antarctica have buffered it, so average temperatures on the continent have changed little in 50 years and the snowpack in the interior has been growing.

Furthermore, Antarctica's ice sits on land, and the warming of even the most gloomy predictions is unlikely to make a big dent in that huge ice pack very soon.

But western Antarctica and the peninsula that juts northward have a different weather scheme. The air over the Antarctic peninsula is one of three places on the globe with the fastest heating; Arctic western Canada and Alaska and the high mountains of China and Tibet are the others. The sea water also is heating, accelerating the breakup of ice shelves that stick out over the sea. When they go, the glaciers on land behind them begin to accelerate their slide to the sea, adding to global sea levels.

"We thought the Southern Hemisphere climate is inherently more stable," Scanbos said. But "all of the time scales seem to be shortened now. These things can happen fairly quickly. A decade or two decades of warming is all you need to really change the mass balance.

"Things are on more of a hair trigger than we thought."