Ice-free Arctic: Not 'If' but 'When'

March 17, 2007

Courtesy of  Far North Science
By Doug O'Harra
The overall trend for Arctic Ocean sea ice cover has declined every month for 27 years in a loss driven both by natural cycles and the steady rise in greenhouse gas concentrations.

Supercomputing climate models - where scientists wrestle a universe of data about human emissions and weather through a galaxy of equations - now show uncanny matches to the real world of floes and open leads.

All this cogitation conjures a startling scenario: the Arctic Ocean will soon be free of ice during late summer, possibly as soon as 2040 and almost certainly by 2100.

“Given the agreement between models and observations, a transition to a seasonally ice-free Arctic Ocean as the system warms seems increasingly certain,” according to new review by senior climate scientist Mark Serreze and researcher Julienne Stroeve with the National Snow and Ice Data Center, and Marika Holland from the National Center for Atmospheric Research.

“The unresolved questions regard when this new arctic state will be realized, how rapid the transition will be, and what will be the impacts of this new state on the Arctic and the rest of the globe.”

And don’t be thinking in terms of some glacial, geologic-speed shift.

“This transition to a new arctic state may be rapid once the ice thins to a more vulnerable state,” the three authors write in Perspectives on the Arctic’s Shrinking Sea-Ice Cover, published March 16 in the journal of Science.

Serreze calls it a “tipping point” that may trigger a cascade of climate change across the globe.

“When the ice thins to a vulnerable state, the bottom will drop out and we may quickly move into a new, seasonally ice-free state of the Arctic,” he said in a followup release from the University of Colorado at Boulder. “I think there is some evidence that we may have reached that tipping point, and the impacts will not be confined to the Arctic region.”

Satellite observations taken this winter continue to show the same downward trend, Stroeve added in an email message.

For the third cold season in a row, the ice did not rebound, suggesting another summer of record or near record lows lies ahead. Temperatures have been well above normal over most of the Arctic Ocean so far this season, with February temperatures about 5 degrees warmer, she said. West of Greenland, temperatures were 10 degrees above normal.

And the sea ice? The 2007 winter cover remains about 7 percent below the average extent seen between 1979 and 2000 - just like the winters of 2005 and 2006.

For Alaskans and other people who gather resources from Arctic seas, the message is plain:

Prepare for a different climate.

“Many of the large ice losses we’ve been seeing in the summer are occurring in the western Arctic and thus certainly directly affect people in Alaska, especially those intimately tied to the sea ice,” Stroeve added. “From what I can see in the observations, the loss of sea ice in this region is likely to continue.”

Since I believe that many of the changes we’re seeing today in the Arctic (and not just the sea ice, but also changes in the tundra, terrestrial and marine ecosystems) are a result of greenhouse gas warming, I think the people of Alaska need to consider adapting (both socially and economically) to continued warming.

The stunning decline of sea ice across the Arctic Ocean during the first years of the 21st Century has become the most dramatic harbinger of worldwide climate change. Other signals include melting glaciers and warming permafrost, greening tundra and ailing boreal forests.

The loss of ice has already begun to disrupt Native subsistence life and expose coastal communities to devastating storms and erosion. (See Shishmaref story.) It it continues as projected, it could eventually threaten the existence of marine mammals like polar bears, walrus and seals. With the projected disappearance of this frozen habitat, the U.S. Fish and Wildlife Service is now taking comments on a proposal to protect polar bears under the Endangered Species Act.

The extent of Arctic sea ice has been shrinking month-to-month, on average, since 1979. Between 2001 and 2006, each September delivered record or near record declines, suggesting to some scientists that the meltdown may be speeding up.

During the five days centered on Sept. 21, 2005 - the general period when sea ice reaches its annual minimum and starts refreezing - the ice pack covered only 2.05 million acres. That left hundreds of miles of mostly open water off northwest Alaska and Far Eastern Russia and beat the previous record of open Arctic water set in 2002. The pack was also smaller than previous low-ice periods of the 1930s and 1940s.

The 2006 extent was just a bit larger, but still covered less ocean than any previous autumn on record before 2005. The Arctic Ocean has lost one-fifth of the average September ice cover observed by satellites between 1979 and 2000.

A seasonal marine habitat about the size of Alaska has simply disappeared.

Winter sea ice has declined too, though at a slower rate. Between 1979 and 2000, sea ice covered about 6 million square miles at the height of winter, but it’s been falling about 3 percent per year. This March, satellites recorded about 5.6 million square miles of ice cover.

While many factors contribute to the ice loss - warm water creeping north from the Bering Sea and Atlantic Ocean, changes in air circulation, thinning floes that don’t rebound in winter - overall warming across the Arctic appears to be a growing influence.

“The sea ice cover seems to be rapidly changing and the best explanation for this is rising temperatures,” said Serezze when the ice set a record in 2005. “My view is it’s getting increasingly difficult to argue against the notion that what we’re seeing is a greenhouse gas effect taking hold.”

In the Science review, the three authors discuss the current understanding of the factors influencing sea ice decline. Air temperatures have varied but largely gone up. Arctic currents that circulate the ice pack in a vast gyre north of Alaska have changed. Continent-size stretches of thick multi-year ice has been flushing out of the Arctic Basin into the Atlantic Ocean through the Fram Strait between Greenland and Svaalbard. Immense slugs of warmer water have surged into the Arctic.

The process feeds on itself:

In general, (greenhouse gas loading) results in a stronger and longer summer melt season, thinning the ice and exposing more of the dark … ocean surface that readily absorbs solar radiation. Autumn ice growth is delayed, resulting in thinner spring ice. This thin ice is more apt to melt during the next summer, exposing more open water, which results in even thinner ice during the following spring.

Sorting out why that’s happened - and whether it’s triggered primarily by human emissions of greenhouse gases or by natural variations - is a complex problem that has not been completely settled. But the three scientists say recent climate models suggest a human influence.

Computer models that analyze the past few decades recreate the similar sea ice declines when the scientists include the “forcing” by human produced greenhouse gases. Hold the gases constant, and the natural ups and downs seen in previous periods for sea ice return.

Climate research has further to go. Supercomputing programs still have a “large spread” in their predicitions of sea ice extent, wrote Holland in an email message. Scientists need to tune them up and evaluate which ones best represent the natural processes out there on the ocean.

The models also need to improve how they handle predictions of greenhouse gas emissions, as well as how they represent natural polar processes, like the release of super-greenhouse gas methane from melting permafrost, she said. “This is an ongoing effort and many models have dramatically improved in quite a short time.”

“The take home message from my perspective is that a human influence on the Arctic’s shrinking sea ice cover is a lock, and that as we continue to lose ice, we will start to see effects extending beyond the Arctic,” Serreze told Far North Science in an email message.