I know I shouldn’t really be surprised by anything in the climate change debate, but I can’t help but be flabbergasted by the recent discussion about the supposed Arctic sea ice recovery. This started with an article by David Rose in the Mail on Sunday claiming that we’re heading for a period of Global cooling. This was then repeated in the Telegraph. This all appears to be based on the observation that the September Arctic sea ice extent this year (2013) is an increase of 60% on that of last year.
I know this has already been covered by Dana in the Guardian and by Sou over at HotWhopper, but I thought I would add my own two cents worth. Firstly, the claim that the Arctic sea ice has “recovered” because this September’s sea ice extent is a 60% increase on last year is absurb. Last year (2012) was an extreme low, so a 60% increase on that does not bring us back to levels similar to what they were prior to the start of the decline. Furthermore, this is a classic example of regression to the mean. The Arctic summer sea ice extent is not the same year on year. Natural variability means that sometimes it is lower than normal, while at other times it is higher. Consider the figure below. It shows the monthly Arctic sea ice extent anomalies (blue line) and a 12 month running mean. It’s clear that there has been a significant decline since the 1960s but there is still substantial variation. Furthermore, given that the scatter is around the running mean, if you have a particular low anomaly one year, you don’t expect another low the year after. Claiming that a 60% increase on the very low value last September is a “recovery” is absolute nonsense.
Furthermore, some have claimed that the sea ice extent now is the same as in 1971. The figure above only goes to 2010, but given that 2012 was a record low and 2013 is a 60% increase on that, this claim doesn’t appear true. There are, however, some quite low anomalies in the 1970s that appear similar to some more recent values. However, claiming that Arctic sea ice has recover because an extreme high today is similar to an extreme low from the 1970s is also absurd. Natural variation! What is also ignored (despite my attempts to get some to recognise this) is that all of this is based on sea icea area/extent. From an energetics perspective (i.e., how much energy is absorbed in melting Arctic sea ice) it’s the mass/volume that’s important. If you consider the figure below (which I got from Neven’s excellent Arctic Sea Ice Blog), the change in volume/mass is much greater than the change in area. Based on mass/volume it’s even harder to claim that there’s been a recovery (presumably why those who make this claim would rather focus on area than volume).
Another claim is that even if Arctic sea ice is decreasing, Antarctic sea ice is increasing. People think that because they both have the same terms (sea ice) that they’re equivalent. Well, they’re not really. One immediate difference is that an increase in Antarctic sea ice doesn’t cancel the change in albedo due to decreased sea ice extent in the North (i.e., it’s winter in the South). Also, Antarctic sea ice tend to be thinner than Arctic sea ice (or at least this used to be true) and so even if the change in area is the same, the change in volume/mass probably isn’t, especially as the increased Antarctic sea ice will be in the northernmost portions of the region. There’s also natural variability, so an increased amount of Antarctic sea ice this year (or for the last couple of years) doesn’t make a trend. The figure below is from the National Snow and Ice Data Centre and shows that since 1978 there has been a modest positive trend (100000 km2 per decade) in Antarctic sea ice. This is 5 times smaller (in magnitude) than the Arctic sea trend (and that’s the trend in extent, not mass/volume). So, no, increases in Antarctic sea ice have not compensated for decreases in Arctic sea ice.
I don’t really know what else to say. No, the 60% increase in September sea ice this year on last year is not a recovery. No, the sea ice extent this year is not the same as in 1971. No, the increased Antarctic sea ice does not compensate for reduced Arctic sea ice. This is an example of an aspect of the debate that just makes me despair. How can anyone dispute the reduction in Arctic sea ice? It seems indisputable, but people still manage to do so. Is it ignorance? Is it deliberate? Is it unfounded optimism (I don’t really want it to be true either)? I really don’t know and I really don’t know how to deal with people who won’t accept the reality of Arctic sea ice decline.