Follow-up: NASA Sees Arctic Ocean Circulation Do an About-Face


A few days ago, I wrote about a new NASA study that suggests that the Arctic Ocean is reversing the circulation direction. The study theorized that the circulation direction was a major contributor of the melting of Arctic ice.

At the time that I wrote the article, there was very little analysis by other scientists on the study (still isn’t). So I reached out to several of the contributors at RealClimate and asked them what they thought.  Dr. Benestad replied to me and he has agreed to let me reproduce his comments here for all to learn from. I would like to publicly thank him for his willingness to help us understand this.

This study doesn’t come as a surprise – the Arctic has undergone pronounced variations in the past. Notably, the ‘early century warming’ in the 1930s. It’s well-known that both the ocean circulation and the atmospheric winds undulate, meander, change coarse, or reverse at time scales from days to decades, due to non-linear chaotic actions, mutual coupling, etc. Nobody serious in this game suggest that all the change in the Arctic is due to AGW (the question is rather, how large fraction is due to AGW?). It’s interesting how the new observations are made – by pressure gauges at the sea floor (the only caveat is the short length of the record: 2002-2006).

The statement ‘The Arctic Oscillation was fairly stable until about 1970, but then varied on more or less decadal time scales’ is debatable, but it’s true that during the last decades, it has been in a more positive and persistent mode. But then, GCMs with increasing GHGs also predict an upward trend in the AO and the AAO (southern hemisphere), so it’s hard to tell wether the change in the AO is natural or man-made (on top of that, there is ozone loss in the stratosphere, etc).

That there has been a trend in the Arctic, I am in no doubt:  e.g. see



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