Arctic sea ice hits second-lowest level - NASA

The extent of sea ice covering the Arctic Ocean in September declined to the second-lowest extent on record, according to satellite data released recently from NASA and the NASA-supported National Snow and Ice Data Center (NSIDC). The Arctic ice cap grows each winter as the sun sets for several months and shrinks each summer as the sun rises higher in the northern sky. Each year the Arctic sea ice reaches its annual minimum extent in September. It hit a record low in 2007. The near- record ice-melt followed higher-than-average summer temperatures, but without the unusual weather conditions that contributed to the extreme melting of 2007.

“Atmospheric and oceanic conditions were not as conducive to ice loss this year, but the melt still neared 2007 levels,” said NSIDC scientist Walt Meier in a statement. “This probably reflects loss of multiyear ice in the Beaufort and Chukchi seas as well as other factors that are making the ice more vulnerable.”

Joey Comiso, senior scientist at NASA’s Goddard Space Flight Centre said the continued low minimum sea ice levels fits into the large-scale decline pattern that scientists have watched unfold over the past three decades.

“The sea ice is not only declining, the pace of the decline is becoming more drastic,” Comiso said. “The older, thicker ice is declining faster than the rest, making for a more vulnerable perennial ice cover.”

While the sea ice extent did not dip below the 2007 record, the sea ice area as measured by the microwave radiometer on NASA’s Aqua satellite did drop slightly lower than 2007 levels for about 10 days in early September, Comiso said.

Sea ice “area” differs from extent in that it equals the actual surface area covered by ice, while extent includes any area where ice covers at least 15 percent of the ocean.

Arctic sea ice extent on Sept. 9, the lowest point this year, was 4.33 million square kilometers. Averaged over the month of September, ice extent was 4.61 million square kilometers. This places 2011 as the second lowest ice extent both for the daily minimum extent and the monthly average. Ice extent was 2.43 million square kilometers below the 1979 to 2000 average.

This summer’s low ice extent continued the downward trend seen over the last 30 years, which scientists attribute largely to warming temperatures caused by climate change. Data show that Arctic sea ice has been declining both in extent and thickness. Since 1979, September Arctic sea ice extent has declined by 12 percent per decade.

Climate models have suggested that the Arctic could lose almost all of its summer ice cover by 2100, but in recent years, ice extent has declined faster than the models predicted.

Scientists warned that the massive amounts of greenhouse gases from thawing permafrost will accelerate and amplify global warming, according to a study in Wednesday’s journal Nature.

Those heat-trapping gases under the frozen Arctic ground may be a bigger factor in global warming than deforestation, said the study based on a survey of 41 permafrost scientists from around the world.

Arctic warming of 7.5 degrees Celsius (13.5 degrees Fahrenheit) this century may unlock the equivalent of 380 billion tons of carbon dioxide as soils thaw, allowing carbon to escape as CO2 and methane.

Scientists predict that over the next three decades, a total of about 45 billion metric tons of carbon from methane and carbon dioxide will seep into the atmosphere when permafrost thaws during summers, which is about the same amount of heat-trapping gas the world spews in five years of burning coal, gas and other fossil fuels.

“Our survey outlines the additional risk to society caused by thawing of the frozen north, and underscores the urgent need to reduce atmospheric emissions from fossil-fuel use and deforestation,” the scientists said. “This will help to keep permafrost carbon frozen in the ground.”

Xinhua