Figure 1. Arctic sea ice reached its minimum on September 16, 2012, and was at its lowest extent since satellite records began in 1979. Image credit: National Snow and Ice Data Center (NSIDC).
by Jeff Masters, via the Wunderblog
The extraordinary decline in Arctic sea ice during 2012 is finally over. Sea ice extent bottomed out on September 16, announced scientists at the National Snow and Ice Data Center (NSIDC) on Wednesday.
The sea ice extent fell to 3.41 million square kilometers, breaking the previous all-time low set in 2007 by 18%–despite the fact that this year’s weather was cloudier and cooler than in 2007. Nearly half (49%) of the icecap was gone during this year’s minimum, compared to the average minimum for the years 1979 – 2000.
This is an area approximately 43% of the size of the Contiguous United States. And, for the fifth consecutive year–and fifth time in recorded history — ice-free navigation was possible in the Arctic along the coast of Canada (the Northwest Passage), and along the coast of Russia (the Northeast Passage or Northern Sea Route.)
“We are now in uncharted territory,” said NSIDC Director Mark Serreze. “While we’ve long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur. While lots of people talk about opening of the Northwest Passage through the Canadian Arctic islands and the Northern Sea Route along the Russian coast, twenty years from now from now in August you might be able to take a ship right across the Arctic Ocean.”
When was the last time the Arctic was this ice-free?
We can be confident that the Arctic did not see the kind of melting observed in 2012 going back over a century, as we have detailed ice edge records from ships (Walsh and Chapman, 2001). It is very unlikely the Northwest Passage was open between 1497 and 1900, since this spanned a cold period in the northern latitudes known as “The Little Ice Age”. Ships periodically attempted the Passage and were foiled during this period. Research by Kinnard et al. (2011) shows that the Arctic ice melt in the past few decades is unprecedented for at least the past 1,450 years.
We may have to go back to at least 4,000 B.C. to find the last time so little summer ice was present in the Arctic. Funder and Kjaer (2007) found extensive systems of wave generated beach ridges along the North Greenland coast, which suggested the Arctic Ocean was ice-free in the summer for over 1,000 years between 6,000 – 8,500 years ago, when Earth’s orbital variations brought more sunlight to the Arctic in summer than at present. Prior to that, the next likely time was during the last inter-glacial period, 120,000 years ago. Arctic temperatures then were 2 – 3°C higher than present-day temperatures, and sea levels were 4 – 6 meters higher.