Steve Gorman, Reuters 17 Sep 09;
LOS ANGELES (Reuters) - The Arctic's sea ice pack thawed to its third-lowest summer level on record, up slightly from the seasonal melt of the past two years but continuing an overall decline symptomatic of climate change, U.S. scientists said on Thursday.
The range of ocean remaining frozen over the northern polar region reached its minimum extent for 2009 on September 12, when it covered 1.97 million square miles (5.1 million square km), and now appears to be growing again as the Arctic starts its annual cool-down, the National Snow and Ice Data Center reported.
That level falls 20 percent below the 30-year average minimum ice cover for the Arctic summer since satellites began measuring it in 1979, and 24 percent less than the 1979-2000 average, the Colorado-based government agency said.
This summer's minimum represents a loss about about two-thirds of the sea ice measured at the height of Arctic winter in March. By comparison, the Arctic ice shelf typically shrank by a little more than half each summer during the 1980s and 1990s, ice scientist Walt Meier said.
The lowest point on record was reached in September 2007, and the 2009 minimum ranks as the third smallest behind last year's level. But scientists said they do not consider the slight upward fluctuation again this summer to be a recovery.
The difference was attributed to relatively cooler temperatures this summer compared with the two previous years. Winds also tended to disperse the ice pack over a larger region, scientists said.
"The long-term decline in summer extent is expected to continue in future years," the report said.
The U.S. government findings were in line with measurements reported separately by the Nansen Environmental and Remote Sensing Center in Norway, which reported this summer's minimum ice extent at just under 5 million square km (1.93 million square miles).
Scientists regard the Arctic and its sea ice as among the most sensitive barometers of global warming because even small temperature changes make a huge difference.
"If you go from a degree below freezing to 2 degrees above freezing, that's a completely different environment in the polar region," Meier said. "You're going from ice skating to swimming. Whereas if you're on a tropical beach and it's 3 degrees warmer, you probably wouldn't even notice it."
World leaders will meet at the United Nations in New York on Tuesday to discuss a climate treaty due to be agreed on in December.
MARITIME IMPLICATIONS
The shrinking polar cap poses a loss of crucial habitat for polar bears and has implications for maritime shipping, opening up new routes to navigation.
Once again this year, the Northern Sea Route through the Arctic Ocean along the coast of Siberia opened, enabling two German ships to navigate the passage with Russian icebreaker escorts.
Russian vessels have traversed the passage many times over the years, but the maritime fleets of other nations are showing more interest in the route as the summer thaw expands.
This year, the Amundsen's Channel through the Northwest Passage also opened briefly, as it did in 2008, but the deeper Parry's Channel did not. Both opened in 2007.
Scientists have voiced concern for years about the alarming decline in the size of the Arctic ice cap, which functions as a giant air conditioner for the planet's climate system as it reflects sunlight back into space.
As a greater portion of the ice melts, larger expanses of darker sea water are exposed, absorbing more sunlight and adding to the global warming effect attributed to rising levels of heat-trapping greenhouse gases emitted into the atmosphere by human activity.
Scientists also have measured a thinning of the frozen seas, as older, thicker ice more resilient to warming temperatures gives way to younger, thinner layers that melt more easily in summer.
Scientists monitor Antarctic sea ice as well, but the Arctic is considered a more critical gauge of climate change because more of the northern sea ice remains frozen through the summer, playing a bigger role in cooling the planet.
(Additional reporting by Alister Doyle in Oslo; Editing by Dan Whitcomb and Peter Cooney)
Pause in Arctic's melting trend
Richard Black, BBC News 17 Sep 09;
This summer's melt of Arctic sea ice has not been as profound as in the last two years, scientists said as the ice began its annual Autumn recovery.
At its smallest extent this summer, on 12 September, the ice covered 5.10 million sq km (1.97 million sq miles).
This was larger than the minima seen in the last two years, and leaves 2007's record low of 4.1 million sq km (1.6 million sq miles) intact.
But scientists note the long-term trend is still downwards.
They note that at this year's minimum, the ice covered 24% less ocean than for the 1979-2000 average.
The analysis is compiled from satellite readings at the US National Snow and Ice Data Center (NSIDC) in Boulder, Colorado.
Colder front
Among the reasons for the less drastic melt are that Arctic temperatures have been cooler this year than last, researchers said, and that winds have helped disperse sea ice across the region.
NSIDC scientist Walt Meier said the reasons for the somewhat cooler temperatures this year were not entirely clear yet.
"We had cloudier conditions and low pressure zones in late summer that probably helped keep temperatures down," he told BBC News.
"It's something we need to look at in more detail.
"But it certainly wasn't as warm as 2007, which was in the order of 2-3C warmer than the average in a lot of places."
The question now, he said, was whether 2007 turns out to be a "high-melt blip", or whether 2009 turns out to be a "low-melt blip" - which will not become evident until next summer at the earliest.
What continues to have scientists worried is that a significant proportion of the cover consists of young, thin ice formed in a single winter.
This is much more prone to melting than the older, thicker ice that dominated in years gone by.
"If we get another warm year, anything like 2007, then the ice is really going to go," said Dr Meier.
"And the chances are that at some point in the next few years we are going to get a warm one."
White heat
In recent decades, the Arctic region has been warming about twice as fast as the average for the Earth's surface.
Recently, scientists specialising in reconstructing past temperatures released data showing that the current decade is the warmest in the Arctic for at least 2,000 years.
Melting ice is a "positive feedback" mechanism driving temperature rise faster. Whereas white ice reflects sunlight back into space, dark water absorbs it, leading to faster warming.
The NSIDC team cautions that this is a preliminary analysis and that further melt is possible, though unlikely, this year.
Next month they will publish a full analysis including more details of how temperatures, currents and winds affected the sea ice this summer.
Arctic ice pack at third lowest extent since 1979: US
Yahoo News 18 Sep 09;
WASHINGTON (AFP) – The Arctic sea ice pack thawed to its third smallest size on record during the northern hemisphere summer of 2009, US government scientists said, citing satellite images.
While the sea ice pack at its lowest 2009 point was slightly larger than both the record-low ice pack measured in 2007 and the summer 2008 ice pack, the data confirms a shrinkage trend seen over the past 30 years, the US National Snow and Ice Data Center said in a statement late Thursday.
The Arctic sea ice pack size has fallen sharply since 1979, especially during the summer months, the center said.
As of September 12, the surface of the Arctic sea ice pack was 5.1 million square kilometers (1.97 million square miles), its smallest point of the year.
At the peak of the summer 2007 melt the Arctic sea ice pack measured 4.1 million square kilometers -- a record low -- while the following year at the lowest point it measured 4.5 million square kilometers.
The summer 2009 low point however was still 1.61 million square kilometers (620,000 square miles) less than the annual 1979 to 2000 average ice pack size, the NSIDC said.
The center's glaciologists attributed the difference in the size of the 2009 ice pack compared to the previous two years to prevailing winds blowing in a different direction.
Arctic sea ice melt still heavy, but no record
Yahoo News 17 Sep 09;
WASHINGTON – The summer melt of Arctic sea ice wasn't quite as bad this year as the last two years. But it still ranked as the third biggest melt on record.
The National Snow and Ice Data Center announced Thursday that the Arctic sea ice reached its annual low last week. Ice extended just shy of 2 million square miles. That's 620,000 square miles less than the 30-year average.
But there was more ice this September than the record low set in 2007 — about one-third of a million square miles more. Last year ranked No. 2.
Arctic sea ice is important because it helps moderate warmer temperatures elsewhere. Experts blame global warming for the increased melting of sea ice and fear that eventually no sea ice will survive the summer.
