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    By Andrew C. Revkin
    The New York Times

    Tuesday 12 December 2006

    New studies project that the Arctic Ocean could be mostly open water in summer by 2040 - several decades earlier than previously expected - partly as a result of global warming caused by emissions of greenhouse gases.

    The projections come from computer simulations of climate and ice and from direct measurements showing that the amount of ice coverage has been declining for 30 years.

    The latest modeling study, being published on Tuesday in the journal Geophysical Research Letters, was led by Marika Holland of the National Center for Atmospheric Research in Boulder, Colo.

    The study involved seven fresh simulations on supercomputers at the atmospheric center, as well as an analysis of simulations developed by independent groups. In simulations where emissions continue to rise, sea ice persists for long periods but then abruptly gives way to open water, Dr. Holland said.

    In the simulations, the shift seems to occur when a pulse of warm Atlantic Ocean water combines with the thinning and retreat of ice under the influence of the global warming trend. Scientists ascribe most of that planet-scale warming, including a warming of the shallow layers of the oceans, to the buildup of carbon dioxide and other heat-trapping smokestack and tailpipe gases in the atmosphere.

    After 2040 or so, ice persists in summer mainly around Canada's northern maze of islands and the northern coast of Greenland, a region that always tends to accumulate a clot of thick ice.

    Separately, scientists at the National Snow and Ice Data Center in Boulder found that the normal expansion of sea ice as the Arctic chilled in fall had been extraordinarily sluggish this year, following a pattern seen in recent years. The November average ice coverage was by far the lowest since satellite measurements began in 1979, said Walt Meier, a scientist at the ice center.

    "It's becoming increasingly unlikely that things will be able to turn around," he said. "It would take several very cold winters and cool summers, which seems unlikely under global warming conditions."

    Several experts not involved with the studies said they were significant for human affairs, as well as biology.

    Polar bears will struggle, these scientists said, and so will Arctic people who still go out on sea ice to hunt seals. By contrast, countries and businesses pursuing new shipping lanes, energy supplies and fishing grounds could profit.

    The melting is likely to shift weather patterns, too. More sea ice means colder winters, because frigid winds blowing over ice pick up little heat from the warmer waters below.

    The change will have ramifications beyond summertime, experts said. Having open water each year would mean that almost all ice forming in winter would be freshly frozen and just a yard or so thick.

    This would greatly ease the task of maintaining shipping lanes with icebreaking vessels, said Lawson W. Brigham, deputy director of the Arctic Research Commission, which advises the White House on Arctic matters. Mr. Brigham and other experts said the new research raised the urgency of establishing common standards for protecting the Arctic environment and patrolling shipping lanes. The commission plans to deliver letters to the Bush administration and Congress this week urging them to commit at least $1 million to start work on replacing the country's two aging, ailing polar-class icebreakers.

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    Arctic Sea Ice "Faces Rapid Melt"
    By Jonathan Amos
    BBC News

    Tuesday 12 December 2006

    The Arctic may be close to a tipping point that sees all-year-round ice disappear very rapidly in the next few decades, US scientists have warned.

    The latest data presented at the American Geophysical Union Fall Meeting suggests the ice is no longer showing a robust recovery from the summer melt.

    Last month, the sea that was frozen covered an area that was two million sq km less than the historical average.

    "That's an area the size of Alaska," said leading ice expert Mark Serreze.

    "We're no longer recovering well in autumn anymore. The ice pack may now be starting to get preconditioned, perhaps to show very rapid losses in the near future," the University of Colorado researcher added.

    The sea ice reached its minimum extent this year on 14 September, making 2006 the fourth lowest on record in 29 years of satellite record-keeping and just shy of the all time minimum of 2005.

    "Feedback Loop"

    Dr Serreze's concern was underlined by new computer modelling which concludes that the Arctic may be free of all summer ice by as early as 2040.

    The new study, by a team of scientists from the National Center for Atmospheric Research (NCAR), the University of Washington, and McGill University, found that the ice system could be being weakened to such a degree by global warming that it soon accelerates its own decline.

    "As the ice retreats, the ocean transports more heat to the Arctic and the open water absorbs more sunlight, further accelerating the rate of warming and leading to the loss of more ice," explained Dr Marika Holland.

    "This is a positive feedback loop with dramatic implications for the entire Arctic region."

    Eventually, she said, the system would be "kicked over the edge", probably not even by a dramatic event but by one year slighter warmer than normal. Very rapid retreat would then follow.

    Locally, this would have major consequences for wildlife in the region, not least polar bears which traverse ice-floes in search of food.

    Loss of summer ice would seriously compromise the lifestyles of the region's indigenous peoples, though it could also bring new trading opportunities as sea routes opened up.

    On a global scale, the Earth would lose a major reflective surface and so absorb more solar energy, potentially accelerating climatic change across the world.

    Sooner or Later

    In one of the model's simulations, the September ice was seen to shrink from about 5.9 million sq km (2.3 million sq miles) to 1.9 million sq km (770,000 square miles) in just a 10-year period.

    By 2040, only a small amount of perennial sea ice remained along the north coasts of Greenland and Canada, while most of the Arctic basin was ice-free in September.

    "We don't think that state has existed for hundreds of thousands of years; this is a dramatic change to the Arctic climate system," Dr Holland told the BBC.

    Dr Serreze, who is not a modeller and deals with observational data, feels the tipping point could be very close.

    "My gut feeling is that it might be around the year 2030 that we really see a rapid decline of that ice. Now could it occur sooner? It might well. Could it occur later? It might well.

    "It depends on the aspects of natural variability in the system. We have to remember under greenhouse warming, natural variability has always been part of the picture and it always will be part of the picture."

    The average sea ice extent for the entire month of September this year was 5.9 million sq km (2.3 million sq miles). Including 2006, the September rate of sea ice decline is now approximately -8.59% per decade, or 60,421 sq km (23,328 sq miles) per year.

    At that rate, without the acceleration seen in the new modelling, the Arctic Ocean would have no ice in September by the year 2060.