Arctic Ice: Pausing Rather Than Declining?
The declining Arctic ice cover has been one of the most powerful images of climate change. Most people who follow the debate but who perhaps don’t look at the data, would be excused for holding the opinion that it’s been declining monotonically.
Hence the dire predictions that it will be gone in a few years, if it shouldn’t have gone already. Several years ago I was heavily lambasted by some for daring to say that I didn’t think it would be all gone by 2013!
The Arctic ice has been declining since satellite observations started in 1979 that clearly caught the decline already in progress and probably part of a multi-decadal change.
Now comes a suggestion that Arctic ice is more resilient that was believed. It’s from a recent paper in Nature Geoscience by Tilling at el (2015) called “Increased Arctic sea ice volume after anomalously low melting in 2013.” The headline is that the volume of Arctic sea ice increased by about a third after an unusually cool summer in 2013. Reports went on to say that the unusual growth continued in 2014 and more than compensated for the loss in the three previous tears. Overall it was concluded that changes in summer temperatures in the Arctic have a greater impact on the ice than was thought.
The key graph in Tilling et al (2015) is their figure showing the growth and decline of sea ice volume since 2011. Note that the maximum hardly changes at all over this period and that the minimum ice extent is increasing. Arctic sea ice increasing! This deserves a second look. Click on image to enlarge.
It has been noticed before that the minimum extent of Arctic ice extent hasn’t been changing very much in the past few years leading some to speculate about a so-called ice pause. In fact, a close look at the Arctic ice extent shows that since 1998 it has been pausing more than it has been declining.
Here is the minimum extent since 2007 (millions of sq km) and it can be seen that the exceptionally cold year of 2013 mentioned by Tilling et al (2015) is not that exceptional in terms of ice extent.
It is 2012 that is exceptional which was due to an anomalous summer storm that compacted the ice. After the storm the ice returned to levels of a few years previously. There is no general decrease in minimal ice area 2007 – 2014. Things get more interesting when one considers the 1998 – 2014 period.
Clearly there has been a decline over this period but not a steady one. rather it has been a shift between two so-called ice pauses. Here is the 1998 – 2006 data.
Admittedly it is a relatively short period, only 17 years, but we only have satellite data since 1979 which provides an additional 19 years – a period comparable to that discussed above so one must take seriously both ways of looking at the data. I could speculate that it looks like the Arctic ice wants to be stable but that perturbations in 2007 and 2002 upset it.
The Tilling et al (2015) paper is very interesting in its discussion of interannual variation in Arctic ice parameters. There are clearly longer-term variations as well.
The so-called pause or hiatus in global surface temperature was first discussed after about eight years of unchanging data. The “pause” in minimal Arctic ice extent is now 17 years. Already some scientists are suggesting that it is a statistical figment, to be expected, and soon to disappear. The same thing was said about the global surface temperature hiatus. Is nature trying to tell us something?