A new study from NASA has revealed how Arctic sea ice thinned between the winters of 2004 and 2008.  The study utilized NASA's Ice, Cloud and land Elevation Satellite, known as ICESat, to allow researchers with NASA and the University of Washington in Seattle to, for the first time, measure ice coverage over the entire Arctic basin.

In the winter, Arctic ice thickens due to the sun setting for several months and ocean currents lessening.  In the summer, there are long sunlight-filled days, stronger ocean currents, and wind to melt the ice.  A lot of ice melts each year, but each year some thicker, older ice survives.  This older ice is 9 feet thick, typically, as opposed to the single-year ice which is on average 6 feet thick.

According to the satellite measurements, the ice has been thinning at a rate of 7 inches per year for a total of 2.2 feet in the last year.  Multi-year ice, meanwhile, shrunk by 42 percent.  Ice cover, meanwhile decreased 595,000 square miles -- nearly the size of Alaska's land area.  The new study is much more accurate than previous studies that estimated ice volume based on area. 

States Ron Kwok of NASA's Jet Propulsion Laboratory in Pasadena, leader of the research team, "Ice volume allows us to calculate annual ice production and gives us an inventory of the freshwater and total ice mass stored in Arctic sea ice.  Even in years when the overall extent of sea ice remains stable or grows slightly, the thickness and volume of the ice cover is continuing to decline, making the ice more vulnerable to continued shrinkage. Our data will help scientists better understand how fast the volume of Arctic ice is decreasing and how soon we might see a nearly ice-free Arctic in the summer."

The team says a combination of recent global warming and anomalies in patterns of sea ice circulation are to blame for the melting sea ice.  States Mr. Kwok, "The near-zero replenishment of the multi-year ice cover, combined with unusual exports of ice out of the Arctic after the summers of 2005 and 2007, have both played significant roles in the loss of Arctic sea ice volume over the ICESat record."

A melting ice cap may unlock new oil deposits and shipping routes.  However, it may also have a negative effect on polar wildlife.  Additionally, while Arctic ice (floating on water) will not impact sea levels, a melting Arctic likely means that Greenland's ice cover will melt, likely flooding low lying coastal cities such as New Orleans and Amsterdam.