Of melting ice and rising oceans

Of melting ice and rising oceans

WARMING WORLD A new study suggests that the glaciers in the Canadian Arctic archipelago could lose as much as one-fifth of their volume. Such a melt would add 3.5 cm to the height of the world’s oceans, writes Jonathan Amos

The glaciers of the Canadian Arctic Archipelago will undergo a dramatic retreat this century if warming projections hold true. A new study suggests the region’s ice fields could lose perhaps as much as one-fifth of their volume.

Such a melt would add 3.5 centimeters to the height of the world’s oceans. Only the ice of Greenland and Antarctica is expected to contribute more.

The assessment is reported in the Geophysical Research Letters journal.

“This is a very important part of the world where there has already been a lot of change,” said lead author Jan Lenaerts from Utrecht University, Netherlands.

“And it is all the more important that we talk about it because it has been somewhat overshadowed by all the news of Greenland and Antarctica,” he said.

The Canadian Arctic Archipelago is a vast area, comprising some 36,000 islands. Being so far north, much of region – some 146,000 square kilometers – is covered by glaciers and ice caps (a type of ice field where glaciers flow off in many directions).
Current data indicates all this ice is already thinning at a rapid rate. Gravity measurements from space suggest the annual loss since 2003 has been running at about 70 billion metric tons, and it is accelerating. With snowfall reasonably constant over the period, it appears that melt as a result of the 1-2-degree rise in air temperatures has tipped the ice out of balance.

Arctic amplification

Lenaerts’ team wanted to understand how this retreat might progress in the decades ahead if the warming continues.

They developed a climate computer model for the archipelago that was based on a midrange temperature projection being used for a big upcoming U N global climate report – the Fifth Assessment Report of the Intergovernmental Panel on Climate Change.

First, they ran the model backward to check that it could accurately recreate  conditions seen in the region since the 1960s. They then ran it forward to simulate the possible shrinking and growth of glaciers right up to 2100.

What they found was that the annual ice loss by this date would be running at about 145 billion metric tons, with the north of the archipelago, on and around the likes of Ellesmere Island, experiencing the greatest retreat.

Added to the general atmospheric warming in the region, the researchers also describe an amplification process whereby reduced snow cover on the surrounding tundra and less sea ice in the Arctic Ocean push up temperatures still further.
This is a consequence of darker surfaces absorbing more heat from the sun rather than reflecting it back out into space.

“What we find is that the processes that are currently ongoing will actually continue and be reenforced, so the mass loss will increase in time,” said Lenaerts.

“Our model estimates that in 2100, we have lost about 20 percent of the volume of Canadian Arctic Archipelago glaciers, which is a really large amount. It is equivalent to 3.5 centimeters of global sea level rise.”

Ice2Sea project

The Utrecht study was funded by theEuropean Union’s Ice2Sea project, which aims to tie down some of the major uncertainties that surround the possible contribution to ocean rise from melting in Earth’s cryosphere.

Ice2Sea’s project leader is professor David Vaughan from the British Antarctic Survey. He said the Canadian Arctic Archipelago was an important region for study because it was not very well mapped, was already experiencing major change and because in some places the ice had “its toes in the water,” which meant it was subject to both atmospheric and ocean impacts.

“We’ve got similar systems in Alaska, in Svalbard, in Patagonia and the Russian high Arctic, and we really need to understand them better,” he said.