Scientists also believe they have detected a 9-year cycle for Arctic ice, in which sea ice extent grows for a few years, and then shrinks until the cycle starts again.
Joey Comiso, senior scientist at NASA Goddard Space Flight Center in Greenbelt, Maryland found that the Arctic multi-year ice - ice that survives for several years - is shrinking by about 17.2 percent per decade. Multi-year ice extent, which is defined as areas of the Arctic Ocean where multi-year ice covers at least 15 percent of the ocean surface, is declining by 15.1 percent per decade. The perennial ice area - ice that survives at least one summer - is retreating by 13.5 percent with the extent pulling back by 12.2 percent. The research noted that sea ice area is always larger than the extent, which highlights the dramatic decline of sea ice core.
"The average thickness of the Arctic sea ice cover is declining because it is rapidly losing its thick component, the multi-year ice," Comiso said. "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." The scientist speculates that perennial ice is not declining as fast as multi-year ice, as its decrease over the past three decades has opened new areas that can be covered by seasonal ice in the winter and some of that new ice was able to survive the summer.
NASA said that Multi-year sea ice hit its record minimum extent in the winter of 2008, when it reached a level of just 55 percent of what it was in the late 1970s. By 2011, the extent had grown back by 34 percent, but has dipped this winter to its second lowest extent on record, which covers 32 years.