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SEWARD, ALASKA

On the approach to Exit Glacier in southeastern Alaska, wooden signs mark nearly 200 years of the ice’s retreat. They begin at 1815, about a mile and a half from the ice’s current terminus. That was the end of a several centuries-long cold spell known as the Little Ice Age. Since then, the bluish ice has receded up the valley at an average rate of 13 meters per year.
Scientists are quick to say that glaciers naturally come and go and that no single phenomenon can be pegged with certainty to human-induced climate change. (Exit Glacier began shrinking before the Industrial Revolution greatly increased greenhouse gases, for one thing.)

But the glacier’s retreat is part of a greater trend. Ice fields throughout the region are thinning. The pattern is apparent in other parts of the world as well. With few exceptions, mountain glaciers in Patagonia, the Himalayas, the Alps, the Rockies, and the Andes – are shrinking. As Doug Causey, vice provost for research and graduate studies at the University of Alaska, Anchorage, says, “We have a pretty good idea of what causes ice to melt.”

The world is warming. Average global temperatures have increased by 1.36 degrees F. since the 19th century, according to the Intergovernmental Panel on Climate Change. In the past 50 years, the rate of warming has nearly doubled. The warming trend is even more pronounced at high latitudes. Temperatures in Alaska have risen 3.6 degrees F. in the past half-century. The warmer conditions are changing marine and terrestrial ecosystems and forcing human communities to adapt as well.
Warmer winters have resulted in spruce bark beetles eating through vast tracts of forest. Some wetlands appear to be drying out. Several coastal villages previously protected by sea ice now find themselves exposed to the ocean’s full fury. They’ll have to relocate.

“What’s happening with climate change – it’s not speculation,” says Colleen Swan, a tribal administrator of Kivalina, a 399-person Inupiat community on the Chukchi Sea. “It’s our reality.”

Alaskan glaciers are thinning at a rate of 1.8 meters yearly, according to laser measurements taken from aircraft.

“We’re measuring almost a doubling in the rate of mass loss over the last decade,” says Anthony Arendt, a postdoctoral fellow at the National Aeronautics and Space Administration’s Goddard Space Flight Center.

The ice melting here is raising global sea levels by 0.27 millimeters yearly, nearly double what Greenland ice sheets contribute now, Mr. Arendt says. So while all eyes are on the Greenland and Antarctic ice sheets (which have the potential to raise the ocean level 7 and 5 meters, respectively), glaciers like these are already melting. “In the next century or so, it’s really these small regions, like Alaska and Patagonia, that need attention,” Arendt says.

In the late 1970s, the pattern of prevailing winds and ocean currents here shifted, bringing warmer water into the area. Scientists see this periodic shift as driving some of the changes. But it doesn’t account for everything, they say.

The higher temperatures also appear to be reshaping ecosystems. In the past 15 years, the spruce bark beetle has decimated forests in southern Alaska. Historically, outbreaks of the beetle occur periodically, but this one seems extreme. In some areas, no mature spruce remains alive, says Ed Berg, an ecologist with the US Department of Fish and Wildlife.

Mr. Berg says milder winters – winter temperatures are rising nearly three times as fast as summer – are especially to blame. Cold winters used to keep the beetles in check. But in recent decades, El Niño events (a periodic warming of the eastern Pacific), have become more frequent. Add to that consecutive warm summers – beetles proliferate rapidly after two in a row – and you’ve got a recipe for out-of-control infestation, he says.

Wetlands are changing, too, says Berg, standing ankle-deep in spongy peat moss in the Kenai National Wildlife Refuge. Material from the bottom of this fen – about seven meters down – dates to 13,700 years ago, the end of the last ice age. Now shrubs and trees are encroaching on what has been a peat moss-dominated bog. Cores taken show no evidence of woody plants until the top, or recent decades. Their arrival implies a drying-out, he says.

“It’s a radical change after 15,000 years, to have shrubs come in like this,” he says.

Northern sea ice cover has diminished dramatically in summer, reaching a record low in 2007. The polar bear and its prey, the ringed seal, are maybe the two best-known examples of wildlife hit hard by receding ice. But there are many others. Mollusk-eating walruses also use ice rafts as bases for foraging trips. But as summer ice has shrunk, scientists in Russia and Alaska observe walruses hauling up on land instead. Foraging from land may lessen the food available within swimming distance, says Chad Jay, a research ecologist with the US Geological Survey in Anchorage. It may also lead to overgrazing of grounds within reach.

“If they’re on the ice, they have a greater area they can cover,” he says. With less ice, “we’re seeing a loss of their habitat,” which limits their distribution.

Coastal Alaskan villages find that the vanishing sea ice has left them exposed, and has vastly increased erosion. Shore ice used to protect communities from waves during fall storms. No longer. “When we get our fall storms, the ice is just not there,” says Ms. Swan of Kivalina. Three villages, Newtok, Shishmaref and Kivalina, will have to relocate within 10 to 15 years due to accelerated erosion, says the US Army Corps of En­­gineers. Some 160 other rural communities are at risk from increased erosion.

The ice loss has also affected how native Alaskan villagers hunt. The villagers subsist partially on wild-caught game. Previously, hunters went perhaps 10 miles out on the ice during spring months in search of whales. But the ice has thinned considerably.

“It’s been very dangerous the last few years,” says Enoch Adams, Jr., chairman of the Kivalina relocation plan committee. “We have to watch it more closely than we ever had to.”

One recent study estimates that adapting state infrastructure to climate change will cost around $6.6 billion by 2080 – and probably more, says coauthor Peter Larsen, now with the Nature Conservancy in Anchorage. Alaska Gov. Sarah Palin has convened a climate change subcabinet to advise on adaptation and mitigation efforts.

The key is to be proactive rather than reactive, says Mr. Larsen, an adviser to the effort. “If you spend more to adapt to the change now, you definitely pay for the costs, and then some,” later, he says.

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