Anyway, in quite a few posts back, I mentioned old ice and new ice and the significance of their proportions relative to each other. I found this good online article on (where else) the NSIDC comparing the age of sea ice in the Arctic in the year 1985 and 2011 in March. The image below shows the Arctic basin. The one on the left is in the year 1985 and the right, 2011. The deeper the blue is the older the ice (the thicker the ice is, the older the ice is likely to be right at the bottom, remember?)
A study by Maslanik et al. was found that in 1987, 57% of the ice was at least 5 years old and a quarter of that was at least 9 years old. In 2007, only 7 of it was at least 5 years old and none of it was 9 years old! That's a huge decrease in just 20 years!
So far, in all the posts I've been talking about ice thickness but I never really found a graph to show the changes (other than videos that don't really quantify the thinning of the ice). Here, below, I found a rather simple one where ice thickness has been plotted out. It is probably the average of ice thickness throughout the entire Arctic Basin. The multi year ice is basically ice that's present for a few years and first-year ice is newly formed ice in the recorded year. There is a slight increase from 2006 to 2007 in both types of ice probably because of newly fallen snow cover. Overall, however, there is a decrease in thickness of both types of ice. If you look at the heat graph, you'll find that there's a lot more areas covered in pink in Feb-Mar '08 than in '06.
The reasons for this have been discussed in previous posts but I want to bring up a point that I haven't managed to discuss properly yet. It's generally accepted that the general cause of the decline in extent and thickness of sea ice is due to the warming. However, temperature works together with the North Arctic Oscillation (NAO). That's a pressure system and changes periodically with the shifts in the position of the mid-latitude jet stream. When the jet stream moves up north, sea ice decline increases in rate (Positive phase) and the reverse is true. So even if the climate isn't warming, the movement of the jet stream is natural and depending on whether it's positive a negative phase, extent of sea ice will be affected in the Arctic Basin. And that strong positive signal in the mid 1990s may have been part of the reason why the older ice was exposed and melted, though it's certainly not the main factor.
What needs to be focussed on is that in the early 2000s, the Beaufort Gyre (which is a pressure system in the Arctic, think of a water whirl pool but in the air and affects the ocean and ice circulation pattern in the Beaufort sea). It forms a sort of protection for ice that is within the Gyre's circulation, allowing it to remain for years without melting. However, this ice is melting in the southern end of the Gyre due to warming temperatures and more extensive melting in the summer.
The more pressing matter is that the melting rate is increasing but the recovery rate is slowing down. In the previous post we see that the Arctic sea ice has almost halved in extent and we're not seeing nor expecting any sort of recovery.
I'm trying to find some sort of positive tone to end of this post (unlike the other 10 posts). So here's a graph that's somewhat optimistic (though misleading). The red line shows that the Antarctic sea ice extent is increasing from 1978 to 2011 (just slightly). Through the opposite can be seen in the Arctic according to the graph below. Looking at the red graph, we see that even if the ice extent is increasing, there seems to be huge variations from year to year, signalling that the ice extent isn't stable and that we shouldn't let down our guard on global warming. The Antarctic's ice needs to be watched carefully since most of the ice is locked on land. If the ice shelves collapse, the glaciers behind it will follow and soon, the ice on the Antarctic might be all lost. That is, if the climate warms even further.
So much for a positive ending. But well, we shouldn't be depressed. At least we're starting to do something.
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