Friday, 20 March 2015

Arctic Attacks

Arctic Sea Ice has reached a new record low maximum. The Guardian covers it quite nicely in this article.

Arctic sea ice extent hits record low for winter maximum

In writing a reply to a comment for the article I ended up listing a number of major reasons why the Arctic is under attack. It turns out there's an awful lot of mechanisms and feedbacks that are making Arctic Sea Ice increasingly vulnerable. Off the top of my head I could think of these:

1. Most of the ice is now easily melted first-year ice, which even when it melts is less likely to refreeze, because it doesn't change salinity of the top layer of water much.

2. The Arctic sea surface temperatures are rising, and will be hit harder again, now we are in an El Nino phase; so melting from below is becoming more of an issue. [This is the primary cause of this years record low Arctic Maximum]

3. The increased amount of open water in the Arctic ocean means that Arctic sea ice is being affected more by storms. In the past the ice itself dampened waves; the effects of currents and could distribute the force of storms across the ice pack. Now there are open waves and the structural integrity can't withstand the currents nor storms. One the effects of this is 'flash melting' where stunning amounts of sea ice can suddenly melt by being submerged during a storm (this was a contributory factor to the summer record in 2012).

4. The increased amount of energy in the atmosphere around the Arctic ocean means that storms are becoming more common and stronger.

5. The increased humidity above the arctic has numerous effects. (a) Water vapour is a greenhouse gas and therefore it acts as a positive feedback on melt. (b) Increased cloud cover reduces direct levels of radiation acting as a negative feedback (though it's understood less than (a)). (c) Regular air temperatures above 0ºC means that rain is increasingly likely and rain is a much more effective thermal conductor than air (because water has a much higher specific heat capacity).

6. Arctic melting is starting to reach the coasts of the Greenland and Canadian Archipelago. This means that the multi-year ice is no longer held fast to the land and is therefore more easily transported.

7. Increased outflow and calving from Arctic glaciers, particularly in Greenland adds to the destabilisation of land-fast Arctic sea ice.

8. The opening of the North East Passage and in particular open water from the North Sea to the Bering Strait (separating Alaska and Russia) means that for some of the year actual ocean currents can flow all the way across the Arctic. This, again, increases transport.

9. The increased rate of arctic temperature rises compared with more southerly latitudes means that the northern Jetstream is breaking down (this is different to the Gulf stream of course). The effect is to make  the Jetstream more wavy which allows warmer air to be transported to the Arctic (often raising temperatures by >20ºC) as well as transporting cooler air further south causing major climatic problems in Canada and North America (the Polar Vortex).

So, in short - there's whole set of depressing indicators and feedbacks as the Arctic Sea Ice melts, which is why as a whole it's accelerating.