The Arctic ice has thinned “irreversibly” since 2007, a study says


Arctic sea ice fell dramatically in 2007 and has never recovered. New research suggests the loss was a sea change that is unlikely to be reversed this century, if at all – perhaps evidence of the kind of climatic tipping point scientists have warned the planet could be about to happen when it warms up.

The conclusion comes from three decades of data on the age and thickness of the ice that flows out of the Arctic each year as it flows east from Greenland into the North Atlantic. Scientists from the Norwegian Polar Institute found a clear difference in ice levels before and after hitting an unprecedented low in 2007.

In the years since, the data shows the Arctic has entered what researchers have dubbed a “new regime” — one that has seen a trend towards ice cover that is much thinner and younger than before 2007, they say Researchers. They link the change to rising sea temperatures in the rapidly warming Arctic caused by human emissions of greenhouse gases.

“Our analysis demonstrates the long-lasting effects of climate change on Arctic sea ice,” they wrote in the journal Nature.

Walt Meier, a senior research scientist at the National Snow and Ice Data Center at the University of Colorado at Boulder, compared the 2007 low to a boxer being knocked out. Any punches that lead to it will weaken the fighter, but this biggest punch is too much for the boxer to overcome.

That doesn’t mean that the Arctic ice will be completely destroyed, but that it won’t be able to recover quickly.

“You’re in a new situation, a new equilibrium, where you can’t easily go back to where you were,” says Meier, who was not involved in the new research.

Data on the likely maximum of Arctic sea ice this year, released by the US Ice Data Center on Wednesday, showed recent trends continuing: The 5.64 million square miles of ice coverage observed on March 6 was the fifth smallest on record. This date is six days earlier than the average for the annual Arctic ice maximum.

The new The analysis by scientists at the Norwegian institute draws on data from the Fram Strait, a passage between Greenland and the Norwegian archipelago known as Svalbard through which Arctic sea ice regularly flows on its way to the North Atlantic. Underwater radar systems can record the amount of ice flowing overhead, while satellites and buoys track the ice’s movement and the length of time it spends in the Arctic before it leaves the pole.

The researchers found a dramatic shift in 2007, when the Colorado Ice Research Center reported a record low in sea ice coverage that was 38 percent smaller than normal and 24 percent smaller than the previous record low set in 2005.

Until 2007, they observed sea ice of varying thicknesses and ages, often with bumps and ridges, derived from older ice floes being packed together. But in recent years, ice floes have been smoother and more uniformly thick, an indication that they are younger and more short-lived. That’s worrying for several reasons: a loss of habitat for Arctic creatures and a decline in the albedo effect, where ice reflects sunlight back into space. A less icy Arctic absorbs more heat from the sun.

Overall, ice floes spend 37 percent less time in the Arctic before escaping through the Fram Strait to melt in the Atlantic, or about 2.7 years on average since 2007, the researchers found. The body of ice thicker than 4 meters (about 13 feet) flowing through the strait down more than 50 percent from the record low of 2007.

The research supports previous studies showing losses of almost all of the oldest and thickest ice that once covered the Arctic and that ice floes are circulating more rapidly around the Arctic and through the Fram Strait as the ice sheet sinks.

The study articulates concerns scientists have harbored since the record low in 2007 (and since the break in 2012). Some wondered at the time if this was the beginning of an epic collapse. That didn’t happen, but there wasn’t a significant rebound either.

Researchers have been reluctant to declare possible changes in the Arctic sea-ice system as a whole because ice cover varies so widely from year to year, Meier said. The new study could change that, he said.

“They’re making a pretty good case and putting together a lot of data to say, yes, there’s a fundamental change and we’re in this new regime,” Meier said.

However, some disagree with one of the researchers’ conclusions.

“I’m not convinced it’s irreversible,” said Harry Stern, a mathematician and sea-ice researcher at the University of Washington’s Applied Physics Laboratory. “If you reverse the conditions, you could reverse the changes in ice thickness.”

The study’s authors said that even under the most optimistic global warming and emissions reduction scenarios, this would take a long time. Even if carbon emissions fell to zero sometime in the next 50 years, it would still be decades before the oceans shed all the heat they have accumulated since humans started burning fossil fuels and emitting greenhouse gases.

“As ocean heat content has increased in sea ice-forming areas,” the authors wrote in an emailed response to questions, “we propose that the changes, at least in the current climate, are irreversible.”

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