Dana Nuccitelli has just published an article in the Guardian entitled:
Not only does Dana kindly link to our recent efforts to educate the Daily Mail’s leader writer about the Arctic facts of life. He also does a much better job of explaining the issues than a previous Guardian article about Arctic sea ice volume which we were recently somewhat critical of. This therefore seems like the perfect time to provide an “Arctic Sea Ice Volume 101” lesson for Daily Mail leader writers and their wholly independent “legal eagles”.
Let’s take things one small step at a time shall we. The Daily Mail leader last week starts by saying:
In a major report last year, the Intergovernmental Panel on Climate Change gave a grave assessment of how man-made global warming was rapidly destroying the Arctic ice cap.
Steadily increasing temperatures had made the pack ice contract by up to 12 per cent between 1979 and 2012, leading to rising sea levels which threatened to swamp coastal regions – not to mention endangering stranded polar bears.
By the middle of the century ‘a nearly ice-free Arctic Ocean’ was likely for a large part of the year, the report predicted.
The Mail’s leader writer isn’t very specific about which of the numerous IPCC reports they are referring to , but the Mail’s legal eagle tells us that:
This item was written on the basis of… the 2014 synthesis report by the Intergovernmental Panel on Climate Change – arguably the definitive authority on the subject.
This is a quote from that IPCC report (p4 notes). ‘The annual mean Arctic sea-ice extent decreased over the period 1979 to 2012, with a rate that was very likely in the range 3.5 to 4.1% per decade.’
Given that there are over three decades between 1979 and 2012, the shrinkage of the ice-cap couldn’t have been more than 12 per cent.
This is the first of many “misunderstandings” in the Daily Mail’s leader and their legal eagles response. Here is an extract from Section B.3 “Cryosphere” on page 9 of the IPCC AR5 Working Group 1 Summary for Policy Makers:
The annual mean Arctic sea ice extent decreased over the period 1979 to 2012 with a rate that was very likely in the range 3.5 to 4.1% per decade (range of 0.45 to 0.51 million km2 per decade), and very likely in the range 9.4 to 13.6% per decade (range of 0.73 to 1.07 million km2 per decade) for the summer sea ice minimum (perennial sea ice).
As you can see, the Mail’s “definitive authority on the subject” subject says that “for the summer sea ice minimum” Arctic sea ice extent in fact decreased by more like 12% per DECADE.
Moving on the next paragraph in the Daily Mail’s leader, we are told that:
How interesting then, that the latest analysis of 88million measurements from the European Space Agency’s Cryosat satellite show the northern ice-cap INCREASED by a staggering 41 per cent in 2013 and, despite a modest shortage last year, is bigger than at any time for decades.
whilst the Mail’s legal eagle explains to us that:
This item was written on the basis of a UCL report that formed this story: http://www.dailymail.co.uk/sciencetech/article-3168504/Arctic-sea-ice-boosted-cool-summer-2013-study-reveals.html
That story states that:
Researchers used 88 million measurements of sea ice thickness recorded by the European Space Agency’s CryoSat-2 mission between 2010 and 2014.
The results showed that there was a 14 per cent reduction in the volume of summertime Arctic sea ice between 2010 and 2012 – but the volume of ice jumped by 41 per cent in 2013, relative to the previous year, when the summer was five per cent cooler than the previous year.
Notice that in this article the author is talking about “summertime Arctic sea ice volume” and not “mean Arctic sea ice extent”. Let’s see if instead of trying to compare apples with oranges like the Mail’s leader writer we can in fact compare like with like shall we?
Firstly let us recall (if we can) from our school days that Volume = Area x Thickness. Next returning to the IPCC AR5 WG1 report we need to turn to the technical summary of their full report where in the TS.2.5.3 “Sea Ice” section on page 40 we can read that:
There is high confidence that the average winter sea ice thickness within the Arctic Basin decreased between 1980 and 2008. The average decrease was likely between 1.3 m and 2.3 m. High confidence in this assessment is based on observations from multiple sources: submarine, electromagnetic probes and satellite altimetry; and is consistent
with the decline in multi-year and perennial ice extent.
Now unfortunately for our purposes this decline in thickness is not expressed as a percentage and is in winter rather than summer. Nevertheless it should be readily apparent to all and sundry by now that the thickness of Arctic sea ice has been declining at the same time as its extensiveness. Moving on to page 136 in section 220.127.116.11 “Ice” of the full IPCC WG1 report we find:
There has been a trend of decreasing Northern Hemisphere sea ice extent since 1978, with the summer of 2012 being the lowest in recorded history (see Section 4.2 for details). The 2012 minimum sea ice extent was 49% below the 1979 to 2000 average and 18% below the previous record from 2007. The amount of multi-year sea ice has been reduced, i.e., the sea ice has been thinning and thus the ice volume is reduced.
Following the IPCC’s instructions let’s now move on to page of section 18.104.22.168 “Arctic Sea Ice Thickness and Volume”, where we read that:
For the Arctic, there are several techniques available for estimating the thickness distribution of sea ice. Combined data sets of draft and thickness from submarine sonars, satellite altimetry and airborne electromagnetic sensing provide broadly consistent and strong evidence of decrease in Arctic sea ice thickness in recent years.
That’s followed by many paragraphs of learned discussion, but still no statement of Arctic wide volume decline in percentage terms to keep the Mail’s legal eagle happy.