New observations from a European Space Agency satellite confirm a University of Washington analysis of Arctic sea-ice volume. The findings reveal that the Arctic has lost more than a third of summer sea-ice volume since a decade ago, when a U.S. satellite gathered similar data. Merging the UW analysis and the new ESA satellite observations reveals the summer minimum in Arctic sea ice is one-fifth of what it was in 1980.
According to the UW’s Polar Science Center, sea ice volume is a key climate indicator. However, Arctic sea ice volume cannot currently be observed continuously. Observations from a variety of sources, including satellites and submarines, are all limited in space and time. The UW model enables scientists to estimate sea ice volume changes on a continuous basis by combining observations from a variety of sources.
Axel Schweiger, a polar scientist in the UW Applied Physics Laboratory, said in a news release that the UW model and new satellite observations suggest that their ice loss estimates may have been “too conservative.”
The UW analysis has offered scientists a 34-year monthly picture of what’s happening to the total volume of Arctic sea ice. The model, known as the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS), analyzes weather records, sea-surface temperatures and satellite pictures of ice coverage to calculate ice volume. PIOMAS verifies the results with thickness measurements from submarines that travel below the ice.
Schweiger said that the variability of the ice prevents scientists from using a single observation, such as sea-surface temperatures, to reconstruct an accurate picture of ice loss that covers several decades.
PIOMAS also verifies the results by comparing them to five years of precise ice thickness measurements gathered by a NASA satellite launched in 2003. The specialized satellite, the Ice, Cloud and Land Elevation Satellite (ICESat), collected ice thicknesses across the Arctic until the spring of 2008. Britain’s CryoSat-2 satellite took up the slack in 2010.
The National Snow & Ice Data Center reports that Arctic sea ice extent for January 2013 was well below average. The NSIDC notes that the average sea ice extent for January 2013 was 13.78 million square miles, which is 409,000 square miles below the 1979 to 2000 average for the month. It is also the sixth-lowest January extent in the satellite record. During the month of January, the Arctic added 525,000 square miles of ice, which is slightly higher than average for the month.
“We are now in uncharted territory,” said Mark Serreze, NSIDC director, in 2012, according to The Washington Post. “While we’ve long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur.”
In some circles, however, the UW figures have been widely criticized because of the significant ice loss that they revealed.
Schweiger said the criticism is justified, but he noted that new satellite observations are “very close” to the predictions made by the model.
Schweiger said it is completely normal for the summer ice volume to decrease faster than the area covered because Arctic sea ice is shrinking and thinning simultaneously. However, past trends may not continue at the same pace. Schweiger posited that developing a reliable picture of the past helps scientists understand changes in the Arctic and allows them to better predict future changes in the region.
Schweiger added that the most important question to ask ourselves now is: “What are the processes that are driving these changes in the ice?”
These findings were recently published online in the journal Geophysical Research Letters.