Posts Tagged ‘Sea Ice’

Arctic Sea Ice: A New Minimum, Again

3 September 2012 Leave a comment

The Arctic sea ice extent has reached a new record low with 2 weeks left to go in the melt season. This marks a more than 40% decline in sea ice minimums over the last 40 years.  Moreover, this new record low comes in a series of months and years of perpetual record breaking melt seasons, with the 6 lowest annual sea ice minimums being recorded in the last 6 years.  Until this year, 2007 held the record reaching then-unfathomable minimum of 4.2 million sq.

miles. This was thought to be due to a confluence of several climatological factors coinciding to produce a shockingly high rate of melt. The 2007 event, like most climate change events, was interpolated as an extreme,  once-in-a-lifetime type event. It’s only when the record is re-broken in short succession by an even stronger melt event, that we start to realize this is not a coincident, but a long-term, severe pattern.

Conservative estimates garnered from the IPCC 4AR suggest that we may see an ice-free Arctic sometime in the latter half of this century. The more progressive estimates suggest this may occur by mid-century. Until this year, the most extreme estimates put an ice-free Arctic as decades off.  Now some experts are saying this may happen before the end of the current decade.

What does an ice-free Arctic mean?

Sea Ice is classified by its age: first-year, second-year, and multi-year. First-year ice is what forms every winter. It can be up to ~1 meter thick. Though it’s tough going, most Arctic Class icebreakers are able to break through ice of this thickness. If first-year ice persists through the summer, it becomes second-year ice and can grow up to 2m thick. Anything beyond 2m thickness is generally referred to as multi-year ice and can be up to 20m thick at ice-ridges. Second-year and multi-year ice creates nearly impenetrable ice packs. While first-year ice will always reform during the winter, an ice-free summer would eliminate all multi-year ice. The subsequent summer would only have thinner, first-year ice which is less likely to persist through the summer, making it very difficult for multi-year ice to reform.  If the Arctic was to experience an ice-free summer, it would signify that a dramatic threshold had indeed been crossed. This, in conjunction with the associated changes in albedo, creates a pretty strong positive feedback loop, which may entrench the ice-free pattern for the foreseeable future.

A completely ice-free Arctic is unlikely for several decades, as the thickest and most stubborn ice is landfast against the brutally harsh north shore of Canada. But landfast ice is of  little concern for mariners as its location is known and predictable. It’s the large, thick, drifting ice packs that provide that largest impediments to Arctic access and nautical navigation, and these would be eliminated by an ice-free summer.

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