April 12, 2010
Massive Arctic Ice Cap Is Shrinking
Rate of ice-cap melt has been accelerating since 1985
Close to 50 years of data show the Devon Island ice cap, one of the largest ice masses in the Canadian High Arctic, is thinning and shrinking.A paper published in the March edition of Arctic, the journal of the University of Calgary's Arctic Institute of North America, reports that between 1961 and 1985, the ice cap grew in some years and shrank in others, resulting in an overall loss of mass. But that changed 1985 when scientists began to see a steady decline in ice volume and area each year.
"We've been seeing more mass loss since 1985," says Sarah Boon, lead author on the paper and a Geography Professor at the University of Lethbridge. The reason for the change? Warmer summers.
The High Arctic is essentially a desert with low rates of annual precipitation. There is little accumulation of snow in the winter and cool summers, with temperatures at or below freezing, serve to maintain levels. Any increase of snow and ice takes years.
This delicate equilibrium is easily upset. One warm summer can wipe out five years of growth. And though the accelerated melting trend began in 1985, the last decade has seen four years with unusually warm summers - 2001, 2005, 2007 and 2008.
"What we see during these warm summers is the extent of the melt is greater," says Boon about the results of a five-year remote sensing study that ran between 2000 and 2004.
The white surfaces of snow and ice reflect heat "“ a process known as the albedo effect. Retreating ice exposes dark soil and gravel, which absorb heat and increase the melt rate of ice along the periphery of the cap. But it's not only the edges of the cap that are losing ice. At lower altitudes the ice is thinning as well.
Changes to the Devon ice cap, which covers approximately 14,400 sq. km, could have multiple impacts on everything from ship traffic to sea level.
There has already been an increase in the number of icebergs calving off from outlet glaciers that flow into the ocean. Boon explains that melt water runs between the bottom of the glacier and the ground, creating a slippery cushion that allows the glacier to slide forward more rapidly than it would in colder conditions.
"There are a lot of things we need to consider. One is the iceberg calving and its implications for shipping. These things don't just go away, they float out into the ocean," says Boon. A second area of concern is the contribution of increased glacier melt to rising sea level.
The work of Boon and her colleagues demonstrates the importance of long-term research. Work on Devon Island began in 1961 with researchers from the Arctic Institute of North America, including long-time Arctic scientist Roy 'Fritz' Koerner, who was part of the current study until his death in 2008. This ongoing research, which is continuing thanks to federal International Polar year funding, has created a comprehensive dataset that contributes to the understanding of the complex play between the ice cap, the atmosphere and the ocean.
"We all know long-term studies are important but they are really hard to pay for."
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