Earlier in the northern summer, it looked like the rapid melt of Arctic Sea ice we’ve been seeing over the last several years was happening again, but rather than being a record year, it was merely tracking along the lower side of the distribution of the long term average. Last year, in contrast, the amount of sea ice hit an all time low early in the year and then broke previous records into tiny icy pieces.
One of the reasons last year’s ice melt was so dramatic is that an early storm churned up the ice and got melting going a bit early.
This year, there was no early churning up event, but over the last several days of June and beginning of July, the rate of sea ice melt has suddenly increased dramatically and this year’s track is looking like it may come close to catching up to the previous year’s unprecedented extreme.
To give you an idea, I’ve got three figures I made by taking screen shots from the Chartic Interactive Sea Ice Graph (here).
This interactive chart uses the high quality data from 1979 to the present to produce a spread (the gray area) showing the range of ice at two standard deviations. Here, I’ve plotted the first ten years of that period against the standard deviation (and mean) to show that during the first part of the period in question the sea ice was melting less each year than the entire spread.
The second figure shows the same thing but for ten years near the end of this period, not including last year and this year:
This shows how the standard deviation spread is actually a bit misleading on its own because it does not show the trend of change over time, but this comparison of an earlier ten year period and a recent ten year period demonstrates it dramatically.
Now, have a look at the third graphic, showing last year’s dramatic sea ice drop and the track for the current year so far.
The melting of this ice faster and more completely means there will be more warming of the Arctic sea by sunlight; the ice would reflect more sunlight back into space but open water absorbs more of it. So, the Arctic is warmer than it should be and it is getting warmer than it was, at the same time.
The warming of the Arctic in turn reduces the gradient of heat from the equatorial regions to the poles in the Northern Hemisphere. This causes the Jet Streams do do strange things, which causes Weather Weirding, the non-technical term we apply to … well, to weird weather. You can read about this link in the following two posts:
<li><a href="http://scienceblogs.com/gregladen/2013/06/04/linking-weather-extremes-to-global-warming/">Linking Weather Extremes to Global Warming</a></li></ul>