Climate change rids Arctic of its oldest ice

Scientists say there’s widespread replacement of the Arctic’s most mature ice masses, which show up in this photo as tinged with blue, by much younger, thinner and weaker sheets of ice. (PHOTO BY JANE GEORGE)

RANDY BOSWELL
Postmedia News

The Arctic’s oldest, thickest sea ice — much of which used to survive the year’s warmest months — had all but disappeared by the end of this summer’s near-record meltdown, according to new U.S. analyses that vividly show how the circumpolar region is being transformed by warmer temperatures and other features of climate change.

In reports issued this week by NASA and the associated National Snow and Ice Data Center, the respective teams of U.S. scientists offered end-of-season overviews of the state of the northern cryosphere that emphasized not only the severe shrinkage of the ice cover for the fifth straight year, but also the widespread replacement of the Arctic’s most mature ice masses by much younger, thinner and weaker sheets of ice.

The trend — reinforced by this year’s loss of about 50 per cent of Canada’s rapidly-vanishing, millennia-old Arctic ice shelves along the coast of Ellesmere Island — continues to suggest the likelihood of ice-free Arctic summers in the coming decades, the experts say.

“The oldest, thickest ice [five or more years old], has continued to decline,” states the report from the Colorado-based NSIDC, which points to the Beaufort Sea north of the Yukon-Alaska boundary as a prime area for the loss of old-growth ice. “In essence, what was once a refuge for older ice has become a graveyard.”

That observation recalls warnings issued two summers ago by one of Canada’s top Arctic scientists, University of Manitoba researcher David Barber, who described how “rotten” ice was becoming prevalent throughout Canada’s northern waters, where thicker and more durable ice previously had been the norm.

By the time Arctic ice reached its minimum extent of 4.3 million square kilometres on Sept. 9, it had nearly equalled 2007’s record melt to just 4.13-million-sq.-km.

Arctic ice typically builds to about 14 million sq. km during the winter months. The 30-year average for the end-of-summer ice extent is about half that, around seven million sq. km.

But the decreased extent of September ice cover in recent years provides only part of the picture worrying scientists — even as the same phenomenon heralds new possibilities for Arctic shipping, tourism and oil and gas exploration.

Thinner ice at the end of the summer typically means winter ice buildup takes longer and results, the following spring, in weaker ice masses entering the next melt cycle. That’s largely why, researchers say, in the five years since 2007, the Arctic has experienced the five greatest summer retreats of sea ice since satellite measurements began in 1979.

NSIDC data released this week shows that while more than 30 per cent of the Arctic’s oldest ice survived the summer of 1983, barely five per cent survived the summer of 2011.

“It looks like the spring ice cover is so thin now that large areas melt out in summer, even without persistent extreme weather patterns,” NSIDC director Mark Serreze said in the centre’s summary of the season’s ice losses.

“The oldest and thickest ice in the Arctic continues to decline, especially in the Beaufort Sea and the Canada Basin,” added NSIDC scientist Julienne Stroeve. “This appears to be an important driver for the low sea ice conditions over the past few summers.”

NASA’s statement on Arctic ice echoed the observations from the Colorado institute, highlighting the reduced thickness of the annual freeze-up.

“The sea ice is not only declining, the pace of the decline is becoming more drastic,” said Maryland-based NASA scientist Joey Comiso. “The older, thicker ice is declining faster than the rest, making for a more vulnerable perennial ice cover.”