Sea ice retreat in Arctic worst in thousands of years: study
“The picture is very troubling. We are losing ice very fast”
Canwest News Service
A major international study of Arctic sea ice has concluded that the recent, record-setting retreat is the worst in thousands of years — a conclusion that challenges skeptics’ claims that the meltdown being witnessed in Canada’s North is probably just the latest low ebb in a historical cycle of ice loss and regeneration.
The new study, involving 18 scientists from five countries and to be published in the journal Quaternary Science Reviews, includes data from two Canadian co-authors who interpret historic levels of ice cover from ancient whalebones found throughout the polar region.
Other evidence marshalled in the bid to reconstruct ancient Arctic climate conditions include patterns of driftwood deposit and chemical signatures in seabed sediments and ice cores.
“The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades,” the study states. “This ice loss appears to be unmatched over at least the last few thousand years and (is) unexplainable by any of the known natural variabilities.”
The study’s lead author, Ohio State University polar researcher Leonid Polyak, told Canwest News Service on Thursday that predictable, long-term ice-cover changes linked to fluctuations in the Earth’s orbit mean “we should expect more rather than less sea ice” at this time in history.
“The evidence that we have based on the existing data suggests that the current Arctic warming is probably the strongest since at least the middle Holocene — that is approximately 5,000 years,” he said.
The two Canadian scientists involved in the study — Geological Survey of Canada researcher Arthur Dyke and McGill University archeologist James Savelle — provided data about the distribution of whalebone deposits, primarily from bowhead whales, to help map the extent of Arctic ice cover over the past 10,000 years.
“The bowhead has left the most abundant, hence most useful, fossil record, followed by the walrus and the narwhal,” the study states. “Former sea-ice conditions can be reconstructed from bowhead whale remains because seasonal migrations of the whale are dictated by the oscillations of the sea-ice pack.”
In 2007, the Arctic Ocean ice cover declined from a winter maximum of 14 million square kilometres to an end-of-summer minimum of about four million square kilometres — the biggest retreat of polar sea ice since satellite measurements began about 35 years ago.
Despite strong ice regeneration this past winter, experts say the thickness and volume of Arctic ice has continued to decline over the past decade, pointing the way to ice-free summers in a matter of years.
Last month, the Colorado-based National Snow and Ice Data Center reported that the relatively greater ice extent of the past winter had already diminished so much this spring that the ice is now on course to retreat more than it did during the record-setting meltdown of 2007.
Mark Serreze, who heads the NSIDC’s annual ice-monitoring program, is among the authors of the Science paper.
In a summary of the study, Polyak acknowledged that the whalebones, sediment cores and other “proxies” for past climate pose limitations and can only reveal information, so far, about the extent of ancient ice cover rather than its thickness and volume.
“Underneath the surface, the ice can be thick or thin. The newest satellite techniques and field observations allow us to see that the volume of ice is shrinking much faster than its area today. The picture is very troubling. We are losing ice very fast,” he said.
“Maybe sometime down the road we’ll develop proxies for the ice thickness. Right now, just looking at ice extent is very difficult.”