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Arctic glacier meltdown accelerates

Doug O'Harra

Glaciers in the Canadian High Arctic -- home to about one third of the world's ice outside of the continental sheets of Antarctica and Greenland -- are melting away much faster than anybody realized. Between 2004 and 2009, the frigid runoff from the ice tongues of Ellesmere, Baffin and hundreds of other islands in the Canadian Far North would have filled Lake Erie three quarters full, according to a new study published this week in the journal of Nature.

Toward the end of that period, the accumulated meltdown had surpassed the runoff from the glaciers rimming the Gulf of Alaska and became the greatest single contributor to global sea-level rise outside the continental sheets, the authors say.

"This is a region that we previously didn't think was contributing much to sea level rise," said lead author Alex Gardner, a research fellow at University of Michigan, in this story. "Now we realize that outside of Antarctica and Greenland, it was the largest contributor for the years 2007 through 2009. This area is highly sensitive and if temperatures continue to increase, we will see much more melting."

The study's nine authors hail from universities and agencies in four countries, and include scientist Gabriel Wolken, now at the Alaska Division of Geological & Geophysical Surveys. Dozens of news sites across the world reported on the paper’s publication.

A chilling harbinger of climate change

The melting of ice across the Arctic -- both on land and at sea -- is one consequence of a decades-long warming trend that offers up a chilling harbinger of disruptive climate change to come. 

The extent of Arctic sea has been shrinking, especially during the summer melt season with the obliteration of habitat for species like for polar bears, walruses and seals. In March, sea ice reached its a maximum extent for the 2010-11 season that almost set a new record for its small size. And now the melt season has begun anew.

The loss of summer ice cover accelerates regional climate warming because the darker open water absorbs more heat from the sun than the bright white floes. For this reason and a shift in weather patterns known as the Arctic Oscillation, the Canadian Arctic experienced record ice loss last fall, with open water persisting in Baffin and Hudson bays into December.

But the melting of sea ice doesn't directly contribute to a rise in the ocean any more than dissolving ice cubes cause your cocktail to overflow its glass. Ice is less dense than water. When bobbing ice floes liquefy, they actually take up less space.

In contrast, melting glacier ice does grow ocean volume because it flows off the land into the sea. Glaciologists have increasingly been trying to sort out how much various glacial fields add to the incremental rise of sea level as a way to monitor the impact of climate change and predict what might happen if warming trends continue.

Calculating the rise of sea level can be complicated anyway. For one thing, the ocean's volume expands in size simply by growing warmer.

Another factor: Sea level rise might not be visible along a given shoreline. Sometimes the land is rising in elevation as fast or faster than the sea, especially in places like Alaska where earth is still rebounding from the removal of the immense weight of Ice Age glaciers.

Some scientists say this thermal expansion explained most of the rise in absolute sea level until about 2003, when mountain glacier runoff became the biggest driver. The rise in absolute sea level, which goes up and down year to year, has been averaging about a tenth of an inch per year in recent decades.

Pound for pound, glaciers out-melt the ice sheets

"Ninety-nine percent of all the world's land ice is trapped in the massive ice sheets of Antarctica and Greenland," the authors explained here:

Despite their size, they currently only account for about half of the land-ice being lost to oceans. This is partly because they are cold enough that ice only melts at their edges. The other half of the ice melt adding to sea-level rise comes from smaller mountain glaciers and ice caps such as those in the Canadian Arctic, Alaska, and Patagonia. This study underscores the importance of these many smaller, often overlooked regions.

The scientists used three independent methods to calculate the amount of runoff from the Canadian Arctic mountain glaciers into the ocean. First, they modeled the net loss (or gain) of glacial mass over time -- a common method for monitoring the health of glaciers. But they also deployed some of the most sophisticated space-age tricks in the bag. With the help of NASA's satellite altimetry project, they got a fix on the height and shrinkage glacier surfaces. They also tracked the changes in the nearby gravitational field as ice shrank back.

"Between the periods 2004–2006 and 2007–2009, the rate of mass loss sharply increased from (about 31 billion tons per year to about 92 billion tons per year) in direct response to warmer summer temperatures," the authors wrote.

At 92 billion tons, the Canadian ice loss during that last three-year period was four times larger than the ice loss seen in Patagonia, and about 22 billion tons larger than the loss measured along the Gulf of Aalska, where melt-back has recently slowed down, the authors said.

"The duration of the study is too short to establish a long-term trend, but for 2007–2009, the increase in the rate of mass loss makes the Canadian Arctic Archipelago the single largest contributor to eustatic (or global) sea-level rise outside Greenland and Antarctica."

Because the area is so sensitive to temperature and doesn't get a lot of precipitation, the scientists said the Canadian glaciers would continue to make be a large factor in sea level rise throughout the coming century.

To dissolve another 15 cubic miles of ice 

The details are startling.

Every one degree increase in average air temperature apparently melted away another 15 cubic miles of the glaciers -- equal to a hunk of ice one mile high, three miles wide and five miles long.

"During the first three years of this study, from 2004 through 2006, the region lost an average of 7 cubic miles of water per year," they wrote. "That increased dramatically to 22 cubic miles of water -- roughly 24 trillion gallons -- per year during the latter part of the study."

In just six years, from 2004 to 2009, Canadian glaciers added 1 millimeter to the height of the global ocean -- about four-hundredths of an inch spread over 129 million square miles.

"This is a big response to a small change in climate," Gardner said in the story. "If the warming continues and we start to see similar responses in other glaciated regions, I would say it's worrisome, but right now we just don't know if it will continue."

Contact Doug O'Harra at doug(at)alaskadispatch.com