It’s been a strange year for the Arctic. During the summer, high temperatures melted away vast regions of the Arctic sea ice, opening up the Northwest Passage for the first time. But then this winter has been unusually cold, bringing back large large areas of sea ice. So what’s going on? Is the Arctic recovering, or is Global Warming marching on?
The big problem studying global warming is that the temperatures and local climate can fluctuate. Over the short term, in some regions, you can have unseasonably warm or cold temperatures. Here in Vancouver, we had one of the coldest, snowiest winters I’ve ever seen.
NASA scientists are measuring the long term trends for the ancient perennial sea ice that lasts across several seasons. And this ice seems to be melting away over the years. In the past, this perennial sea ice – anything that lasted more than a single year – covered 50-60% of the Arctic. This analysis was made by NASA’s ICESat satellite, which measures sea ice thickness with microwaves.
This year, the perennial sea ice covered only 30% of the Arctic. And the most ancient ice, that which has survived more than 6 years, used to comprise 20% of the Arctic. Now it’s down to just 6%.
As this year shows, Arctic sea ice doesn’t stand still. Its coverage grows and declines seasonally, reaching the maximum in March, and the minimum in September. And this year, the maximum is up 3.9% over the previous 3 years. At the same time, the perennial sea ice coverage is down to an all-time minimum.
As the perennial sea ice thins, it’s more vulnerable during the summer melt period to wind and waves. Large chunks of ice can be carried out of the Arctic to melt in warmer waters.
Don’t worry about water levels rising as the sea ice coverage disappears. This ice is already in the water, displacing the same amount. So as it melts, sea levels should stay right where they are. That’s different from the ice locked up in the world’s glaciers, Greenland, and the Antarctic ice cap. As those melt, sea levels will rise.
To better understand the Arctic ice coverage, NASA is planning to launch a follow-on mission called ICESat II, due for launch in 2015.
Original Source: NASA News Release