The Atlantic Multidecadal Oscillation (AMO) is a naturally occurring 60-90 year cycle in sea surface temperatures in the North Atlantic. This cycle consists of alternating cold and warm periods and has an influence on the climate in the region. A recent paper by Martin W. Miles, et al, examines the history of ice extent in the area and compares it to the AMO record. What they found is that ice extent in the region fluctuates in response to the changes in the AMO, resulting in periods of greater and lesser ice extent. They suggest that some of the unprecedented loss of sea ice in the recent decades can be tied to a warm cycle in the AMO.
I have no problem with this. I would expect there to be just such a naturally occurring cycle. But, I do not find this to be enough to explain what we have been witnessing, and the authors emphasize that this in only a part of the puzzle and there are other factors, including warming from manmade emissions, that are contributing to the ice loss.
Take a look at the ice anomaly for September 2012:
And the ice extent for the same month:
The Barents Sea is the area on the right, between Norway and the polar sea ice. With the North Pole marked in both images, it is the area at about the 4-5 o’clock position. Comparing the two figures, we can see this region has experienced a great deal of sea ice since 1980. Can the AMO explain all of this loss? I would be not, but let’s say that it is still under study.
But, what about the rest of the Arctic Ocean? There is significant loss all around the North Pole and this cannot be explained by the AMO. So, before we get all excited that maybe the loss of the Arctic sea ice is just a naturally occurring event, we can already see that it may be contributing to the recent loss, but it cannot explain for all of it. After all, we never saw the level get this low in previous warm cycles. And, the current loss began during a cool cycle. Clearly, there is more to the ice loss than the AMO.