NASA has revealed in a study that the old thick Arctic sea ice is disappearing at a faster rate than the young thin ice along the Arctic Ocean edges.
Multi-year ice is the thick Arctic sea ice that survives through at least two summers. With the thicker ice melting just as fast, or even faster than the young thin ice results in the fast disappearance of older thick ice which makes Arctic sea ice even more vulnerable to further melting in the summer.
Joey Comiso, senior scientist at NASA Goddard Space Flight Center, Greenbelt, Md., and author of the study, which was recently published in Journal of Climate said, “The average thickness of the Arctic sea ice cover is declining because it is rapidly losing its thick component, the multi-year ice. At the same time, the surface temperature in the Arctic is going up, which results in a shorter ice-forming season. It would take a persistent cold spell for most multi-year sea ice and other ice types to grow thick enough in the winter to survive the summer melt season and reverse the trend.”
When looking at the two images from NASA from 1980 and 2012 you’ll see how much the ice has melted over the past 30 years. Scientists can differentiate the multi-year ice from the seasonal ice which comes and goes every year just like summer.
Arctic Sea Ice 1980
Arctic Sea Ice 2012
Comiso found that perennial ice, which is defined as all ice that has survived at least one summer, is shrinking at a rate of -12.2 percent per decade, while its area is declining at a rate of -13.5 percent per decade. These declining numbers indicate that the thickest ice, multi-year-ice, is melting faster than the other perennial ice that surrounds it.
The multi-year ice hit it’s record low in the winter of 2008. The Arctic ice reduced by 55 percent of its average since the late 1970’s. Now, the ice did recover a little bit the next three years, but dropped again with the above average temperatures for this winter in 2012. In 2012 the Arctic sea ice hit the second lowest ever.
NASA reported that “Comiso compared the evolution of the extent and area of multi-year ice over time, and confirmed that its decline has accelerated during the last decade, in part because of the dramatic decreases of 2008 and 2012. He also detected a periodic nine-year cycle, where sea ice extent would first grow for a few years, and then shrink until the cycle started again. This cycle is reminiscent of one occurring on the opposite pole, known as the Antarctic Circumpolar Wave, which has been related to the El Niño-Southern Oscillation atmospheric pattern. If the nine-year Arctic cycle were to be confirmed, it might explain the slight recovery of the sea ice cover in the three years after it hit its historical minimum in 2008.”