New Efforts to Predict When Polar Ice Will Melt

The loss of sea ice in the Arctic may have reached a "tipping point" that could "trigger a cascade of climate change" reaching much farther south. As Arctic warming accelerates, polar waters could become ice-free by the turn of the century, or, under one scenario, as early as 2040.

These are among the conclusions of a new study published March 16 in the journal Science. The area of the Arctic covered by sea ice has been shrinking at least since 1979, when regular satellite observations began.

The report attributes the loss of ice, averaging about 38,000 square miles annually (an area about the size of Maine), to rising concentrations of greenhouse gases in the atmosphere, as well as to natural variability.

Says Mark Serreze, a senior research scientist at the University of Colorado's National Snow and Ice Data Center and the lead researcher on the report:

"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. 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."

The effects could be felt widely around the world and could include drought in the American West and increased winter rains over Western and Southern Europe, notes a story in Britain's Telegraph. Dr. Serreze told the newspaper:

"The basic issue is that the Arctic acts as the Northern Hemisphere 'refrigerator' of the climate system. Change the nature of the refrigerator, and the rest of the climate system will respond."

Out of 15 computer models that Serreze and his team studied, about half forecast that sea ice would disappear for at least part of the year by 2100, according to a story about the study in the Los Angeles Times. If you jump in a plane and head north into the Arctic, the change is apparent, the Times says.

"You have to fly a lot longer to get to the ice edge than you used to," says Josefino Comiso, a satellite-imaging expert at NASA's Goddard Space Flight Center, who was not an author of the report. Some experts say that as more ice disappears and turns to open ocean, which absorbs heat more easily, melting will accelerate. Adds Mr. Comiso: "With less and less ice, you have more and more heat."

At the same time, open waters could offer benefits, clearing passageways now blocked by ice for shipping and oil production, notes a story from Reuters. In a report prepared for the US government, the US Arctic Research Commission says:

"Diminishing sea ice conditions in the Arctic Ocean are changing ecosystems, most conspicuously for polar bears. This also creates unprecedented access for ships that will bring people to the north, and will significantly shorten global marine transportation routes."

The Arctic is thought to hold about 25 percent of the remaining oil and gas reserves in the world, which could be easier to reach by sea. But that could also bring added risk of oil spills and the need for new cleanup methods.

"Cleaning up oil in ice is a bear," says Mead Treadwell, the commission chairman.

The Guardian takes note of the Arctic report and adds that scientists in Britain have found four glaciers at the other end of the world, in Antarctica, retreating in unison.

Duncan Wingham at University College in London and Andrew Shepherd at Edinburgh University in Scotland reviewed five years of Antarctic observations and found that the glaciers -- Pine Island and Thwaites on the western Antarctic and Totten and Cook glaciers in the eastern Antarctic -- were retreating in unison, faster than in previous decades. Says Dr. Wingham:

"Although the amounts of water aren't yet that large, the concern is that we simply don't know what's causing this acceleration of [melting in] these glaciers. It may be that warm ocean water is getting underneath them and making them flow more easily."

Earth's poles are very sensitive and "they're experiencing more change compared to what the tropics are," Ross Virginia, a professor of environmental studies at Dartmouth College in Hanover, N.H., told Reuters. The school hosted a summit on the Arctic that ended this week.