This week NSIDC came with its yearly end of the season press release about sea ice. Their title was: Arctic sea ice shatters previous low records; Antarctic sea ice edges to record high. Kudos to NSIDC for mentioning the Antarctic record in their title. As many of you will have noted, the Antarctic sea ice reached about the same amount of sea ice as the record year of 2007. Wait a second, wasn’t 2007 also the year in which the Arctic sea ice reached a record low? Indeed, it was. So for the second time in a row the Arctic record low happened at the same time as the Antarctic record high. Is this a coincidence or is there some magical teleconnection operating between our poles?

Before we get back to that question, first some facts about the (media) attention that both the Arctic and the Antarctic are getting. Let’s do some simple ‘google’ and ‘google news’ searches for “Arctic sea ice” and “Antarctic sea ice”:

Arctic sea ice
Google: 4,220,000
Google news: 3970

Antarctic sea ice
Google: 967,000
Google news: 370

Apparently the Arctic sea ice is more interesting than the Antarctic sea ice, especially for the media. We all knew that: good news isn’t news, bad news is news.

In that sense the balance in the headline of the NSIDC press release is quite remarkable. Their press release itself mainly deals with the Arctic. Only at the end the Antarctic is mentioned:

As the Arctic was experiencing a record low minimum extent, the Antarctic sea ice was reaching record high levels, culminating in a Southern Hemisphere winter maximum extent of 19.44 million square kilometers (7.51 million square miles) on September 26. The September 2012 monthly average was also a record high, at 19.39 million square kilometers (7.49 million square miles) slightly higher than the previous record in 2006. Temperatures over Antarctica were near average this austral winter. Scientists largely attribute the increase in Antarctic sea ice extent to stronger circumpolar winds, which blow the sea ice outward, increasing extent.

NSIDC scientist Ted Scambos said, “Antarctica’s changes—in winter, in the sea ice—are due more to wind than to warmth, because the warming does not take much of the sea ice area above the freezing point during winter. Instead, the winds that blow around the continent, the “westerlies,” have gotten stronger in response to a stubbornly cold continent, and the warming ocean and land to the north.”

But I see this as a step forward. Back in 2007, the same end of the season press release didn’t mention the Antarctic at all.

The NSIDC press release attributes the increase in sea ice around Antarctic to stronger circumpolar winds. About the Arctic decline in sea ice they write:

Scientists attribute this trend in large part to warming temperatures caused by climate change.

So on the North pole we see the symptoms of a global changing climate, but at the Southpole there is a regional cause in play. Now it’s obviously true that there are large differences between the Arctic and the Antarctic sea ice. NSIDC summarizes the differences nicely:

Sea ice differs between the Arctic and Antarctic, primarily because of their different geography. The Arctic is a semi-enclosed ocean, almost completely surrounded by land. As a result, the sea ice that forms in the Arctic is not as mobile as sea ice in the Antarctic. Although sea ice moves around the Arctic basin, it tends to stay in the cold Arctic waters.

The Antarctic is almost a geographic opposite of the Arctic, because Antarctica is a land mass surrounded by an ocean. The open ocean allows the forming sea ice to move more freely, resulting in higher drift speeds. However, Antarctic sea ice forms ridges much less often than sea ice in the Arctic.

So it’s fair to say that the two regions are not easy to compare. Most climate scientists seem to agree that the Arctic sea ice is more vulnerable and therfore a better indicator for climate change. But we will see if this opinion will hold if times change and Antarctic sea ice starts decreasing.

Back to the question whether it is a coincidence that the record low in the Arctic is combined with a record high in the Antarctic. In the last decade there have been some studies about what is called the polar see-saw hypothesis, the idea that climates of the Northern and the Southern hemisphere are out of phase. There even is a wiki page although that one is rather short.

By far the most relevant and interesting paper I found is Twentieth century bipolar seesaw of the Arctic and Antarctic surface air temperatures by Petr Chylek, a wellknown scientist with a slightly skeptical profile.

Their abstract:

Understanding the phase relationship between climate changes in the Arctic and Antarctic regions is essential for our understanding of the dynamics of the Earth’s climate system. In this paper we show that the 20th century de-trended Arctic and Antarctic temperatures vary in anti-phase seesaw pattern – when the Arctic warms the Antarctica cools and visa versa. This is the first time that a bi-polar seesaw pattern has been identified in the 20th century Arctic and Antarctic temperature records. The Arctic (Antarctic) de-trended temperatures are highly correlated (anti-correlated) with the Atlantic Multi-decadal Oscillation (AMO) index suggesting the Atlantic Ocean as a possible link between the climate variability of the Arctic and Antarctic regions. Recent accelerated warming of the Arctic results from a positive reinforcement of the linear warming trend (due to an increasing concentration of greenhouse gases and other possible forcings) by the warming phase of the multidecadal climate variability (due to fluctuations of the Atlantic Ocean circulation).

Their paper suggests there is a strong anticorrelation between the Artic and the Antarctic with a peak of -0.89 when using a 17 year smoothing of the temperature data. Their figure 2a is quite interesting:

Figure 2. (a) De-trended Arctic (blue) and Antarctic (red) temperature time series smoothed by a 11 year running average (thin lines) or 17 year running average (thick lines), and (b) the AMO index [after Parker et al., 2007] annual values (thin line) and 17 year running average (thick line).












So the anticorrelation between the poles seems to have been there for some time. It’s not so easy to come up with a physical mechanism although the high correlation with the AMO seems to indicate an important role for the Atlantic Ocean. Chylek:

The high correlation of the polar de-trended temperature time series with the AMO index suggests that the variability of the Atlantic ocean circulation might serve as a link with the bi-polar temperature seesaw pattern. The observed seesaw pattern is consistent with the model of the interhemispheric ocean circulation that includes a strong upwelling along the Antarctic Circumpolar Current.

To conclude I think much more research should focus on this highly intriguing anticorrelation between the Arctic and the Antarctic. But this probably will only start when a shifting AMO really reverses the trend on both poles.


0 0 stemmen
Artikel waardering