A question was asked recently:
Sorry, it’s not about Arctic not Antarctic, but the Arctic thread seems to be already closed for commenting. There’s a thing I can’t understand about Arctic sea ice – how come according to NSIDC the maximum sea ice extent in 2013 was the 6th lowest in satellite history while Jaxa is showing it to be higher than the 2000’s (not even 2010’s) average?
The short answer is: in the JAXA plot, the line labelled “2000’s Average” isn’t the 2000’s average.
We’ve already examined the big picture of global temperature according to the recent reconstruction for the holocene (in particular the last 11,300 years) from Marcott et al. We also took a close look at the recent uptick in temperature. Now let’s see about some of the regional differences indicated by these data.
In their supplemental materials, Marcott et al. included the reconstructions restricted to three very wide latitude bands: the northern extratropics (from 30N latitude to the N.Pole), the southern extratropics (from 30S latitude to the S.Pole), and the equatorial band (from 30S to 30N latitude). These reconstructions are computed using their “Standard 5×5” method. But we noted that they may suffer from a difficulty, that as time marches forward, the drop-out of more and more proxies can lead to spurious jumps in the average temperature. This is especially difficult for the most recent time period, because that’s when there are the fewest proxies remaining (so things are less accurate anyway) and there’s more proxy drop-out.
In the last post we looked at the recent temperature reconstruction for the holocene, in particular the last 11,300 years, from Marcott et al. We noted that the changes over most of this very long time span were no bigger, but a lot slower, than the changes over the last century or so. That means trouble.
We also mentioned that the “uptick” at the end of their “main” (the “Standard 5×5”) reconstruction was much larger than in their RegEM reconstruction, and that they had expressed doubt about its robustness. The large uptick at the end (in 1940) is larger than indicated by the instrumental data — another reason to doubt its reality. Let me tell you my opinion why this difference exists. I could be mistaken, but this is what I think.
There’s a new reconstruction of past temperature covering the last 11,300 years by Marcott et al. (2013, A Reconstruction of Regional and Global Temperature for the Past 11,300 Years, Science, Vol. 339 no. 6124 pp. 1198-1201, DOI:10.1126/science.1228026). Data for their reconstructions, and the proxy data on which they’re based, are part of the supplementary materials.
The Marcott reconstruction has been joined to the Shakun reconstruction prior to that, and the HadCRUT4 global temperature data since, and the projected temperature change under the A1B scenario for the future, by Jos Hagelaars, in order to show us some perspective on climate change past, present and future.
This graph has been dubbed the “wheelchair.” Compared to the past, what’s happening in the present is scary. The future is scary as hell.
We’ve looked at Arctic sea ice data, noting not only its overall decrease but changes in the annual cycle as well. As one reader suggested, let’s take a similar look at sea ice in the southern hemisphere.
It is real.
And it’s caused by man
atmospheric carbon dioxide
Having looked at extent, area, and volume of Arctic sea ice, then at its thickness, let’s examine some other derived variables.
In the last post we looked at the extent, area, and volume of Arctic sea ice. We also mentioned that we can derive other quantities from these, namely the average thickness as the volume divided by area, and what I called the “spread” which is the extent divided by the area. I’ve also been looking at the difference (rather than ratio) of sea ice extent and area, which I’ve dubbed the “split” (for lack of a better term). I’ll take up spread and split in another post, at the moment let’s see how thickness has changed over time.
Although it’s useful and sometimes interesting to refute silly ideas about Arctic sea ice loss (such as the claim that it is “stabilizing” or even in “recovery”), it’s far more interesting scientifically to consider what available data actually tell us about the changes of the ice pack in the frozen north.
NOTE: for a brief, non-technical summary of this post see the UPDATE at the end. To get there, go to the full post (not just the blog’s home page), then click here.
Real data are the combination of signal and noise. By noise I don’t just mean measurement error. I mean the stochastic part of the process. That includes naturally occuring noise in the system itself — those ubiquitous wiggles up and down and up and down and down and up, that never cease but never really get anywhere. They’re not part of the trend, they’re noise. If you want to know what the trend is then you have to account for the noise.
If you claim that “ice cover is stabilising,” then you better be talking about the trend. You damn well better not be basing that conclusion on the effect of those ubiquitous wiggles that never cease but never get anywhere.