Steve Gorman, Reuters 6 Apr 09;
LOS ANGELES (Reuters) - Arctic sea ice, a key component of Earth's natural thermostat, has thinned sharply in recent years with the northern polar ice cap shrinking steadily in surface area, government scientists said on Monday.
Thinner seasonal sea ice, which melts in summer and freezes again every year, now accounts for about 70 percent of the Arctic total, up from 40 to 50 percent in the 1980s and '90s, the researchers said, citing new satellite data.
At the same time thicker ice, which lasts two summers or more without melting, now comprises less than 10 percent of the northern polar ice cap in winter, down from 30 to 40 percent. Just two years ago, the thicker so-called perennial sea ice made up 20 percent or more of the winter cap.
Scientists have voiced concerns for years about an 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 into space.
As a greater portion of the ice melts, it is replaced by darker sea water that absorbs much more sunlight, thus adding to the warming of the planet attributed to rising levels of heat-trapping greenhouse gases emitted into the atmosphere by human activity.
"The ice cover plays a key role in the climate," Thomas Wagner, the chief snow and ice scientist for NASA, said in a conference call with reporters. "The thicker ice particularly is very important, because it's the thicker ice that survives the summer to stay around and reflect that summer sunlight."
Walter Meir of the National Snow and Ice Data Center in Boulder, Colorado, added, "We're getting an ice cover as we finish the winter and head into summer that's much more vulnerable to the summer melt and much more likely to melt completely and expose that dark ocean."
The decade-long trend of a contracting ice cap around the North Pole is continuing as well.
The maximum extent of Arctic sea ice for the winter of 2008-09 was measured at 5.85 million square miles (15.2 million square km), the fifth-lowest winter peak on record. That tally represents a loss of some 278,000 square miles (720,000 square km), about the size of Texas, from the winter peak averaged from 1979 to 2000.
The six lowest measurements since satellite monitoring began in 1979 have all occurred in the past six years.
Still, the total volume of sea ice in the Arctic during winter is estimated to contain enough water to fill Lake Michigan and Lake Superior combined.
Meir said there are consequences of an Arctic thaw beside a speed-up of global climate change and the survival of wildlife that depend on the polar ice.
Vanishing summer ice will open new navigation routes for shipping, opportunities to develop the region's natural resources and competition among northern nations to lay claim to parts of the Arctic, he said.
Meir said a strong consensus has emerged among climate scientists that the Arctic is headed for its first largely ice-free summer in the relatively near future, with forecasts running as early as 2013, though he sees that as too soon.
In any case, he added, "It's not a matter of if, it's a matter of when."
(Editing by Bernie Woodall and Vicki Allen)
Arctic sea ice thinnest ever going into spring
Seth Borenstein, Associated Press 6 Apr 09;
WASHINGTON – The Arctic is treading on thinner ice than ever before. Researchers say that as spring begins, more than 90 percent of the sea ice in the Arctic is only 1 or 2 years old. That makes it thinner and more vulnerable than at anytime in the past three decades, according to researchers with NASA and the National Snow and Ice Data Center in Colorado.
"We're not set up well for summertime," ice data center scientist Walt Meier said Monday. "We're in a very precarious situation."
Young sea ice in the Arctic often melts in the spring and summer. If it survives for two years, then it becomes the type of thick sea ice that is key. But the past two years were warm, and there's more young, thin ice at the top of the world.
In normal winters, thick sea ice — often about 10 feet thick or more — extends from the northern boundaries of Greenland and Canada almost to Russia. This year, the thick ice cap barely penetrates the bull's-eye of the Arctic Circle.
The amount of thick sea ice hit a record wintertime low of just 378,000 square miles this year, down 43 percent from last year, Meier said. The amount of older sea ice that was lost is larger than the state of Texas.
"That thick ice really traps ocean heat; it keeps the planet in its current state of balance," said Waleed Abdalati, director of the Center for the Study of Earth from Space at the University of Colorado and NASA's former chief ice scientist. "When we start to diminish that, the state of balance is likely to change, tip one way or another."
Sea ice is important because it reflects sunlight away from Earth. The more it melts, the more heat is absorbed by the ocean, heating up the planet even more, said NASA polar regions program manager Tom Wagner. That warming also can change weather patterns worldwide and it alters the ecosystems for animals such as polar bears.
The Arctic essentially acts as a refrigerator for the rest of the globe. And the amount of sea covered by ice — thick or thin — has been shrinking at a rate of about 3 percent a decade in the Arctic.
This year, the maximum ice cover of 5.85 million square miles — reached on Feb. 28 — was higher than four of the previous five years. But it was still the fifth lowest since record-keeping began in 1979.
Usually, younger, thin ice accounts for about 70 percent of the ice cover. This year it reached 90 percent, Meier said.
And the problems of global warming caused melt is being seen at the other pole, too.
The U.S. Geological Survey last week released a detailed map of the Antarctic coastline and found dwindling and even disappearing ice shelves.
The map itself was finished in the middle of last year, but the previous Interior Department didn't want to release it and other Antarctic maps, said map co-author Richard Williams Jr., a glaciologist for the USGS. The report with the map bears the 2008 date and the previous interior secretary's name on it.
The map shows found for the first time that an entire ice shelf — the Wordie ice shelf on the western end of the Antarctic peninsula_ has essentially disappeared. In 1966, it was 772 square miles. In addition, about 4,500 square miles of the Larsen ice shelf is gone.
"The map portrays one of the most rapidly changing areas on Earth, and the changes in the map are widely regarded as among the most profound, unambiguous examples of the effects of global warming on Earth," the USGS report concludes.
Arctic ice thinner than ever: scientists
Yahoo News 6 Apr 09;
WASHINGTON (AFP) – The Arctic ice cap is thinner than ever, satellite observations revealed Monday, while also indicating that the sea ice cover continues to shrink due to global warming.
This winter saw the fifth lowest maximum ice extent on record since monitoring by satellite began in 1979, said the Colorado-based National Snow and Ice Data Center (NSIDC).
The period between 2004 and 2009 saw the lowest ice extent, said Charles Fowler, a University of Colorado (CU) glaciologist who led a team of scientists for the research.
The researchers found that the maximum sea ice extent for 2008 and 2009, reached on February 28, was 5.85 million square miles (15.2 million square kilometers), 278,000 square miles (720,000 square kilometers) less than the average extent between 1979 and 2000.
"Ice extent is an important measure of the health of the Arctic, but it only gives us a two-dimensional view of the ice cover," said Walter Meier, research scientist at the NSIDC and CU.
"Thickness is important, especially in the winter, because it is the best overall indicator of the health of the ice cover. As the ice cover in the Arctic grows thinner, it grows more vulnerable to melting in the summer."
Until recently, most Arctic sea ice survived at least one summer and often several. But the situation has changed dramatically, according to the scientists.
Thin seasonal ice, which melts and refreezes every year, now makes up about 70 percent of Arctic sea ice in wintertime, up from 40 to 50 percent in the 1980s and 1990s.
Thicker ice (9 feet, or 2.74 meters) that survives at least two summer seasons now only accounts for 10 percent of wintertime ice cover, down from 30 to 40 percent, the researchers said.
Last year, a team of researchers led by Ron Kwok of NASA's Jet Propulsion Laboratory in Pasadena, California, mapped for the first time sea ice thickness for the entire Arctic basin.
Kwok said that older, thicker sea ice is declining and being replaced with newer, thinner ice more vulnerable to melting in the summer, the US space agency noted in a statement.
A team of three British explorers on February 28 set out on an 85-day, 850-kilometer (530-mile) trek to the North Pole to measure the thickness of sea ice along the way.
Global warming is believed to be the main culprit in the rapidly melting north polar ice cap that is freeing up new sea routes and untapped mineral resources on the ocean bottom.
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