Historical climatology in Greenland

However, there is a bit of a cottage industry of people who micro-parse every new paper to see how it projects onto a narrow view of the climate change debate regardless of their actual relevance. This is a travesty of the way science is supposed to work and all too often ends up getting the story completely wrong. One persistent abuser of this technique is Pat Michaels, and in a recent piece he was unable to resist claiming that the century-scale trends (~0.8 C from 1891-1900 to 1991-2000 in the annual mean) seen in this extended Southern Greenland data apparently invalidate the notion of polar amplification as predicted by the ‘models’. This of course was not the conclusion of the authors themselves (though presumably if they felt that this was true they might have said so).

So what is wrong with this claim? Firstly, models do indeed predict polar amplification (particularly in the Arctic and particularly in winter) of global warming trends (see our previous piece on this concept) in general. But do they predict it for the 20th Century trend? and specifically in Southern Greenland? Michaels doesn’t enlighten us, preferring generalized vague statements to actual data-model comparisons.

Indeed, the dampened late 20th century winter warming over a substantial part of Greenland, particularly the western and southern regions emphasized by the network of stations analyzed by Vinther et al, is known (see e.g. this NOAA page) to be associated with a trend toward the positive phase of the Arctic Oscillation (‘AO’) pattern. Whether or not this latter trend can, in turn, be related to anthropogenic climate change is not yet agreed upon, but a plausible argument for this has indeed been made in the peer-reviewed literature. Nonetheless, even if the substantial recent trend in the AO pattern is simply a product of natural multidecadal variability in North Atlantic climate, it underscores the fact that western and southern Greenland is an extremely poor place to look, from a signal vs. noise point of view, for the large-scale polar amplification signature of anthropogenic surface warming. This is a fairly basic point.

What would a rational data-model comparison look like? Since the data show southern Greenland temperatures over the last 150 years, it would be most useful to look at model simulations for exactly that period, run with the best guesses for CO2, solar and volcanic forcing etc. Fortunately, over 20 model groups have deposited these simulations in a public database at PCMDI – and anyone who is actually interested in seeing what the models produce can have access (you need to register, but it’s just a formality).

What do they show? Interestingly enough, the models do not predict large trends in the vicinity of Southern Greenland over the last 100 or so years (the figure shows the ensemble mean results just from the GISS model, but others are similar). Mainly this is because these areas are relatively close to both open water and the ice sheet and that keeps temperatures pretty stable. Like a glass of water with ice cubes, any extra energy tends to go into melting rather than temperature changes. And in this region, changes in the AO pattern discussed above also appear to play some role. (It should also be noted that the trends in this region are not larger than the standard deviation, and so any one realisation is likely to have a lot of variability, as is seen in the observations).

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