A science blogger named Tamino, in a post he made here, challenged me to “explain it or shut up” related to the loss of northern hemisphere Arctic ice this season which he claimed was …” undeniable, that it’s not natural variation” in contrast to the southern hemisphere Antarctic setting a new record for ice extent. While I suspect that sea ice is not his specialty, nor is it mine, I will bring some things to the attention of my readers available from literature.
Just last Monday, NASA was quietly issuing a press release explaining why Arctic sea ice loss was so great this year. (h/t Douglas Hoyt).
From the release: A team led by Son Nghiem of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., studied trends in Arctic perennial ice cover by combining data from NASA’s Quick Scatterometer (QuikScat) satellite with a computing model based on observations of sea ice drift from the International Arctic Buoy Programme. QuikScat can identify and map different classes of sea ice, including older, thicker perennial ice and younger, thinner seasonal ice.
“Unusual atmospheric conditions set up wind patterns that compressed the sea ice, loaded it into the Transpolar Drift Stream and then sped its flow out of the Arctic,” said Son Nghiem of NASA’s Jet Propulsion Laboratory and leader of the study. When that sea ice reached lower latitudes, it rapidly melted in the warmer waters.
In simpler terms, polar wind patterns changed and blew sea ice further south to warmer waters than it normally would. Sea ice can easily be wind driven.
I wonder if that’s the same mechanism that caused loss of Arctic sea ice in the 1920-30′s?
The Arctic is almost as warm now as it was seventy years ago. Unsurprisingly, Arctic ice has diminished. But, as Polyakov et al.show, the long-term changes are “generally statistically insignificant”. But there’s more ice in Antarctica now. It seems that points more to a natural, cyclical variation on a global scale when one pole diminishes while another gains.
Then there’s area to consider, as commenter Aaron wells writes:
According to Cryosphere Today, normal North Pole ice area at this time is about 5 million km^2, with current amounts amounting to a negative anomaly of about 2 million km^2, for a current total of about 3 million km^2. On the other hand, the South Pole normal area is about 15 million km^2, with current amounts amounting to a positive anomaly of 1 million km^2, for a current total of about 16 million km^2.
Now, it is easy to get alarmed about the North Pole numbers, because they have gotten so close to zero. But the truth is about 2/3rd of total North Pole ice always melts by the end of the northern summer. This summer it got down to about 1/4 of the winter amount.
It is much less alarming if you consider the total between the 2 poles. Using the Cryosphere Today normals and current ice areas, there is normally about 20 million km^2, and currently there is only 19 million km^2. When you realize that the total taken together only represents about a 5% reduction from normal, then it does not seem nearly as alarming.
Arctic = 3 million square kilometers – shrinking, new record low
Antarctic = 16 million square kilometers – growing, new record high
Net change in ice area 5%
Polyakov concludes: A combination of century- and half-a-century-long data records and model integrations leads us to conclude that the natural low-frequency oscillation (LFO) exists and is an important contributor to the recent anomalous environmental conditions in the Arctic. This mode of oscillation is related to fluctuations in the thermohaline circulation in the North Atlantic [Delworth and Mann, 2000]. Comparison of the century-long NAO index time series and half a century time series of the polar region SAT, SLP differences, and wind vorticity index shows the existence of the LFO mode in the latter time series. There is evidence that the LFO has a strong impact on ice and ocean variability. Our results suggest that the decadal AO and multidecadal LFO drive large amplitude natural variability in the Arctic making detection of possible long-term trends induced by greenhouse gas warming most difficult.
It appears that there is precedence for what we are observing today, and a strong suggestion of a cyclical nature that points to a natural variability mechanism. Plus, the most important thing to note is that we only have satellite measured sea ice data from about 1979. A 30 year trend isn’t enough to conclude much upon, especially when there is clear evidence of a larger period cycle.
Of course, I don’t expect Tamino will pay any attention to any of this, since he’s made it clear that he’s no longer going to listen to anything “deniers” (as he’s labeled those with contrasting views) have to say. That’s OK, I enjoyed the research.