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Alaska Glaciers Help Drive Rise In Sea Level
Geophysical Institute researcher Regina Hock & her colleague Valentina Radic have calculated that the rate of sa-level rise due tthe meltwater from glaciers in Alaska and elsewhere will increase by as much as 60 percent by the year 2100. Half of the world's smallest glaciers may not survive that long.
Many glaciers smaller than about 5 square kilometers - like those in the European Alps, New Zealand, Scandinavia and Glacier National Park in Montana will disappear by the end of this century, said Radic, a researcher at the University of British Columbia & former graduate student at the Geophysical Institute. She & Hock authored a paper on their meltwater calculations that appeared in Nature Geoscience on January 9, 2011.
According tRadic and Hock, the contribution trising sea level from melting glaciers outside the massive ice sheets in Antarctica and Greenland will grow by the end of the century tabout 1.6 millimeters per year from the current 1 millimeter per year.
"This is significant even though the total over 100 years (around 12 centimeters or 4.6 inches) may not sound like much," Hock said.
The expansion of ocean water resulting from warmer air is responsible for about one-quarter of the world's current sea-level rise of approximately 2.5 millimeters each year (roughly 1/10th of an inch). Additional rise is attributed tmeltwater coming from ice that formed during colder periods of Earth's past. Currently, about half of the water gushing tthe sea from glaciers comes from Alaska & mountainous areas other than Antarctica & Greenland.
Radic and Hock wanted tsum up how much water the world's smaller bodies of ice were contributing tsea level rise because other scientists had overlooked - mountain glaciers like those in Alaska and Canada. Even though Antarctica & Greenland account for 99% of all the ice-bound water on the planet, the meltwater from smaller glaciers has caused about 40% of recent sea-level rise.
"(It's) because they are in warmer climates," Hock said of rivers of ice like Alaska's Yakutat Glacier, which formed at such a low elevation that warmer air is now causing it tdisappear. "The Greenland & especially the Antarctic ice sheets are smuch colder. It doesn't matter if the climate there warms from minus 40 tminus 35; the ice still won't melt.
But it makes a lot of difference for glaciers - where temperatures are around the freezing point (which includes most of those in Alaska)."
Radic & Hock used 10 global climate models tpredict changes in
120,000 of the world's mountain glaciers. They calculated that the twmain contributors tglobal mountain glacier and ice cap shrinkage by 2100 would be Alaska and arctic Canada. Alaska will lose 40% of its glacier ice volume in that time, according tsimulations, and the European Alps & New Zealand will lose three-quarters of their glacier ice.
Predictions for an increased rate of smaller glaciers turning intocean are conservative, Radic and Hock wrote, because they dnot account for the water in icebergs from glaciers that calve intthe sealike Columbia, Hubbard, & hundreds of others in Alaska. In these tidewater glaciers, loss of glacial ice tcalving sometimes exceeds the amount that melts.
Scientists have not come up with an accurate method tquantify that ice loss, but Hock's colleagues at the Geophysical Institute are getting closer tan answer as they study the "icequakes" caused by calving ice at glaciers in southern Alaska.
This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell is a science writer at the institute.
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