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.

The Big Wedgie

This is just a short blog about an interesting development in the Arctic. I keep a frequent lookout on websites such as NSIDC's Arctic Sea Ice News and importantly Neven's Sea Ice Blog.

One of the big predictions for forthcoming years is the collapse of the Arctic ice cap which may happen as soon as in just a few years. This graph makes it quite clear what will happen:

It's a scary graph and implies that we'll have a September minimum of 0Km3 as early as 2015; an August ... October minimum of 0Km3 as early as 2016 and a July minimum of 0Km3 as early as 2017. That is, a rapid collapse of the Arctic sea ice. However, there are wide error bars, and so future predictions should be treated cautiously.

In the arctic much of the ice disappears every year (first year ice), but some remains (multiyear ice). The resilience of Arctic sea ice depends upon multi-year ice, because it's thicker. Most of the multiyear ice was lost in 2007 and has progressively depleted since then.

As you can see, most of the remaining multi-year ice (about 20% of ice >=4 years) clings to the North Coast of Greenland and islands North of Canada and the thinking is that any ice that clings on beyond 2016 or so will be there. This might not happen. Here's why. There's regular arctic ice being churned out from the Fram Strait, the sea between Greenland and Svalbard thanks to Arctic ocean currents that head up North round  from the Atlantic (the same currents that give the UK warm weather).  You can see it here:

It's thought by some Arctic observers that the multi-year ice is held in place at the top of Greenland by what's called the Wedge. This may get swept out through the Fram strait in just a couple of days. It'd be the big Wedgie for the Arctic and would have serious consequences for the remaining multi-year ice and whether the Arctic sea ice would in fact trend to around 1MKm3 or nothing at all. Here's a model of the process:

The reason why it can get swept out now, is because the ice is so thin elsewhere in the Arctic, on average, it's just over 1metre thick. Since we know that with thinner ice sea currents have more opportunity to influence Arctic sea ice and in recent weeks observers have noticed a number of cracks appearing in the Arctic sea ice, early than they would be expected (large cracks do occur in the ice, just not normally this early, here):

(It's a false-color image so you can see the contrast more easily, Greenland is bottom right, cracks are shown white against orange).
Of course, it might not actually happen - I'll post a comment in a few days if it does!