Perhaps the most obvious “turning point” in Arctic sea ice is the stunning decline at the summer minimum of 2007. The annual minimum extent for every year since then has been less than for every year before then. To many, it marks a new era for the ice pack covering the Arctic ocean. The post-2007 era has been makedly different from what happened before.
But if you look at the annual minimum of Arctic sea ice volume rather than extent, the decline has been more consistent. There was indeed a large decrease in 2007 with no year post-2007 as high as any year pre-2007 — but there was also a dramatic decline in 2010 with no year post-2010 reaching pre-2010 levels.
Was there a qualitative change in the ice pack in 2010, one which might rival the qualitative change in 2007?
An interesting quantity to study is the ratio of the volume of Arctic sea ice to its area (volume data from PIOMAS, area data from Cryosphere Today). In a sense this is a measure of average thickness, but it doesn’t include areas of open sea so it’s the average thickness only for areas which have at least some ice. Still, it shows a consistent decline over the years.
We can use windowed Fourier analysis to study many quantities, including the annual-mean ratio of volume to area. This too shows the decline, revealing just how dramatic it has been. It also shows that the change in 2010 was greater than in previous years, so when it comes to thinning of the ice pack 2010 seems to be the “turning point” year.
We can also look at the timing of the seasonal cycle of volume/area ratio. One way is to examine the phase (time of year) of the maximum point of the fundamental Fourier component of the seasonal cycle. Although there’s a steady decline prior to 2010, with the peak coming earlier in the season, it isn’t until 2010 that we see a truly dramatic change.
It’s not just the timing of the seasonal cycle which has changed, its very shape has been transformed. And, the change during 2010 was stunning, with no year post-2010 matching any year pre-2010.
The Arctic is changing dramatically, right before our eyes. Not only did the extent and area “fall through the floor” in 2007, the volume did so in both 2007 and 2010. And the very shape of the seasons has changed, in ways that may not be reversed for a very long time, if ever. In those terms, 2010 far exceeds 2007 in its stunning impact.
And then there’s 2012.
Click the graph!