Poles apart: A record-breaking summer and winter | Arctic Sea Ice News and Analysis
...While much attention has been paid to the record minimum Arctic ice extent set on September 16, 2012, winter sea ice extent in Antarctica has reached a record high. The Antarctic extent increase is an interesting response to changes in circulation patterns in the Southern Hemisphere.
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As the Arctic was experiencing a record low minimum extent, the Antarctic was reaching record high levels in the satellite record, culminating in a 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.
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Our colleague, Dr. Sharon Stammerjohn of INSTAAR, University of Colorado, provides a review of the differences between Arctic and Antarctic climate controls on sea ice and helps place the events in context. First, climate is warming over much of the Antarctic continent, as shown in several recent studies (e.g., Steig et al., 2009) and is related to Pacific Ocean warming (Ding et al., 2010) and circumpolar winds. Both warming and ozone loss act to strengthen the circumpolar winds in the south. This is due primarily to persistently cold conditions prevailing on Antarctica year-round, and a cold stratosphere above Antarctica due to the ozone hole. Stronger winds generally act to blow the sea ice outward, slightly increasing the extent, except in the Antarctic Peninsula region, where due to geography, winds from the north have also increased, pushing the ice southward. Thus, sea ice extent near the northwestern Antarctic Peninsula continues to decline rapidly, while areas in the Ross Sea and the southern Indian Ocean show significant increases (Stammerjohn et al., 2012). Circumpolar-averaged sea ice extent changes nearly cancel each other out for all months of the year (Parkinson and Cavalieri, 2012). This winter, atmospheric conditions were near average overall, with roughly equal areas of cooler and warmer air temperatures over the sea ice.
Comparing winter and summer sea ice trends for the two poles is problematic since different processes are in effect. During summer, surface melt and ice-albedo feedbacks are in effect; winter processes include snowfall on the sea ice, and wind. Small changes in winter extent may be a more mixed signal than the loss of summer sea ice extent. An expansion of winter Antarctic ice could be due to cooling, winds, or snowfall, whereas Arctic summer sea ice decline is more closely linked to decadal climate warming.
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