Arctic sea ice decline “exceeds expectations”

A new study has provided numbers that say what everyone in the Arctic already knows: the season for sea ice is shortening.

Using NASA satellite images, a group of scientists has measured the first day of the spring melt and the first day of the fall freeze each year since 1979.

In Hudson Bay and some other areas in other countries, melt season has grow longer by 10 to 11 days each decade according to lead researcher Thorsten Markus, a geologist with NASA Goddard Space Flight Centre.

“The changes that we are seeing in the Arctic are just mind-blowing,” he said. “It exceeds everybody’s expectations.”

The timing of sea ice formation and melt can vary a lot from year to year due to weather and tides and the combination thereof. But by looking over a long period of time, Markus and his team were able to discern a clear trend across much of the Arctic.

The seas are frozen for a shorter part of the year than in the past.

That’s particularly true for areas where most of the ice is fragile, first-year ice that forms every year, such as Hudson Bay and the Beaufort, Chukchi, Laptev and East Siberian seas.

Especially when covered in snow, sea ice reflects a lot of sunlight and heat. But when the seas are thawed or there’s water sitting on top of the ice, it absorbs more sunlight and heat.

That creates a positive feedback loop where the melting seas exacerbate their own changes.

“People once predicted ice-free summers (in the Arctic) by the end of the century,” Markus said. “Now (scientists predict) 2030 or even 2020.”

In only four areas was the melting trend unclear after statistical analysis of the wildly fluctuating data: the Sea of Okhostk and the Bering Sea.

Aside from Hudson Bay, Canadian Arctic waters lost four to five days of sea ice season per decade since 1979.