Arctic ice loss has been much worse historically: study

A chunk of spruce, typical of driftwood on the northern shore of Greenland, being sawn up for identification and carbon-14 dating. Scientists say the wood probably originated in forests in the drainage area of Canada’s Mackenzie or Yukon rivers about 2,000 years ago, and was carried by ice on a 5,000-km trip across the Arctic Ocean to Greenland. (PHOTO COURTESY OF SCIENCE/AAAS)

MARGARET MUNRO
Postmedia News

The meltdown underway in the Arctic is remarkable, but an international team of beachcombers has uncovered evidence it’s been much worse before.

Driftwood from Canada, Alaska and Siberia picked up on the planet’s most northern beaches indicates that, for several thousand of the past 10,000 years, there was at least 50 per cent less sea ice in the Arctic than there is today, the team reports Friday in the journal Science.

Open water used to crash ashore on Greenland’s northern beaches, which are now locked in ice year-round, say the scientists, who have weathered fierce summer snowstorms on their beachcombing expeditions.

While the researchers say they expect global warming will eventually make the Arctic sea ice disappear, they say the dire warnings about its imminent demise have been overstated.

“The bad news is that there is a clear connection between temperature and the amount of sea ice,” says lead author Svend Funder, at the University of Copenhagen, adding there is “no doubt” continued global warming will reduce Arctic summer sea ice.

“The good news is that even with a reduction to less than 50 per cent of the current amount of sea ice, the ice will not reach a point of no return,” says Funder, who has headed several treks to the inhospitable north coast of Greenland to get a better read on how the ice waxes and wanes.

Satellite records showing how the ice grows and retreats only go back to early 1979 — and suggest 2011 could see another record ice loss.

But the Greenland north coast provides valuable long-term perspective, with the driftwood and sand on the beaches recording ice trends that go back 10,000 years.

Between 8,000 to 5,000 years ago, when the temperatures were warmer than today, Funder and his colleagues report, there was probably less than 50 per cent of the summer 2007 ice coverage, which was the lowest in 30-year satellite record.

During the pre-historic warm period, they say, the southern limit of Greenland’s year-round sea ice was about 1,000 kilometres north of where it is today.

The data was gathered on beaches, which are now locked behind ice that lasts all year on the northern coast of Greenland. But ridges along the beaches, dating back thousands of years, show that waves used to break along the coast, indicating plenty of open water, report the scientists, who mapped beach ridges extending 500 kilometres along the coast.

The driftwood is even more telling, revealing when the ice returned and how it moved around.

Funder said the wood had to have been carried in on ice. That’s because it would take several years for wood to make it across the Arctic Ocean and “driftwood would not be able to stay afloat for that long.”

The most direct route is from central Siberia, with larch from the Siberian forest arriving in Greenland after a trip on the ice lasting two to five years.

“The voyage form North America is more precarious,” the researchers say, because the wood had to go from the Beaufort Sea and then make a detour around past Siberia, increasing the travel time to six years or more. (Ice travels around the Arctic counter-clockwise.)

Spruce from Canada and Alaska started showing up on the Greenland beaches about 6,000 years ago, and increased with the climatic cooling that then occurred, Funder said via email.

He said spruce makes up about 40 per cent of all the driftwood, “which at first glance is surprising” considering that the travel route is much longer than from Siberia.

“The reason is probably that with its longer residence time in the Arctic Ocean the American ice grows to be very thick and therefore a more robust wood-carrier than the thinner Siberian ice with its much shorter passage,” he said.

Funder said the results support the idea that sea ice could regenerate even if it’s reduced to half its current amount. But reversing the current ice loss, he said, “will require that global warming is brought to a halt, or at least slowed down significantly.”

While some scientists have predicted the Arctic could be ice free by the summer by 2030 or earlier, Funder said he expects the summer ice could last until the end of the century. His team’s finding also indicates the wind plays a large and under-appreciated role in shifting ice around, which could slow the loss.

Meanwhile, ice watchers report that Arctic sea ice hit a new low in July.

The sea ice extent reached the lowest level for the month in the 1979 to 2011 satellite record, even though the pace of ice loss slowed substantially during the last two weeks of July, the U.S. National Snow and Ice Data Centre reported Wednesday.

It said shipping routes in the Arctic have less ice than usual for this time of year, and new data indicate that more of the Arctic’s store of its oldest ice disappeared.