Alaska: Climate-change frontier
Melting glaciers, drier wetlands, warmer winters in Alaska, where global warming is felt most keenly.
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.)
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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.
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.