Alaska glaciers help drive rise in sea level

Release Date: 
Wednesday, January 12, 2011

An Alaska researcher and her colleague from the University of British Columbia have calculated that the rate of sea-level rise due to the meltwater from glaciers in Alaska and elsewhere will increase by as much as 60 percent by the year 2100, and that half of the world’s smallest glaciers won’t survive until then.

Many glaciers smaller than about five 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 Valentina Radic of the University of British Columbia, formerly a graduate student at the University of Alaska’s Geophysical Institute. She and the Geophysical Institute’s Regine Hock authored a paper that appeared in Nature Geoscience on Jan. 9, 2011.

Radic and Hock calculated that the contribution to rising sea level from melting glaciers outside the massive ice sheets in Antarctica and Greenland will grow by the end of the century to about 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 much,” Hock said.

Expansion of ocean water by warmer air leads to about one-quarter of the world’s current sea-level rise of about 2.5 millimeters each year (about 1/10th of an inch). The rest is meltwater coming from ice that formed during colder periods of Earth’s past. About half of the water now gushing to the sea from glaciers comes from Alaska and other mountainous areas outside Antarctica and Greenland.

Radic and Hock wanted to sum up how much water the world’s smaller bodies of ice, such as mountain glaciers in Alaska, Canada and elsewhere, were contributing to sea level rise because other scientists had overlooked them. Even though Antarctica and Greenland account for 99 percent of all the ice-bound water on the planet, the meltwater from smaller glaciers has caused about 40 percent 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 making it disappear. “The Greenland and especially the Antarctic ice sheet are so much colder. It doesn’t matter if the climate there warms from minus 40 to minus 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 and Hock used 10 global climate models to predict changes in 120,000 of the world’s mountain glaciers. They calculated that the two main contributors to global mountain glacier and ice cap shrinkage by 2100 would be arctic Canada and Alaska. Alaska loses 40 percent of its glacier ice volume in that time, according to their simulations, and the European Alps and New Zealand lose three-quarters of the ice now in mountain glaciers.

Their predictions for the increased rate of smaller glaciers turning into ocean was conservative, Radic and Hock wrote, because they didn’t include the water in icebergs from glaciers that calve into the sea, like Columbia, Hubbard, and hundreds of others in Alaska. In these tidewater glaciers, loss of glacial ice to calving sometimes exceeds the amount that melts. Scientists have not come up with a great way to quantify that ice loss, but Hock’s colleagues at the Geophysical Institute are getting closer as they study the “icequakes” caused by calving ice at glaciers in southern Alaska.

CONTACT: Ned Rozell, GI information officer, 907-474-7468, nrozell [at] gi [dot] alaska [dot] edu