The SI Weather
3Dec/13Tue

12:15 PM | Global sea ice areal extent at highest level since 1994; southern hemisphere continues on an amazing run

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The southern hemisphere sea ice areal extent continues its recent impressive run at daily record high levels when compared to all prior years in the satellite record-keeping era which began in 1979. This stretch of daily record high sea ice areal extent in the southern hemisphere has actually been occurring for the past several weeks. In fact, the southern hemisphere sea ice areal extent has had quite an amazing run during the past few years from below normal levels to the current well above normal values (above map courtesy University of Illinois "cryosphere"). On a global basis, sea ice areal extent is currently above normal and, in fact, has now reached levels not seen since around 1994 - thanks in large part to the happenings in the southern hemisphere.

The northern hemisphere sea ice areal extent is still below normal for this time of year although it has gained significantly compared to one year ago. In general, the northern hemisphere sea ice areal extent has been at below normal levels since the mid 1990’s. Two distinct trend lines can be seen in the northern hemisphere sea ice areal extent dating back to 1979. First, the northern hemisphere sea ice areal extent featured an “above normal” and general “sideways” trend until the mid 1990’s and then, following that point in time, there has been an overall downward trend to the current below normal values. This directional change in trend during the mid 1990’s correlates quite well with a northern Atlantic Ocean sea surface temperature cycle that is tracked by meteorologists through an index called the Atlantic Multidecadal Oscillation (AMO). Indeed, the Atlantic Ocean has a significant impact on northern hemisphere sea ice and the AMO index flipped in phase during the mid 1990’s from negative (cold) to positive (warm), and the northern hemisphere sea ice areal extent has been in a general downward trend ever since. Once the northern Atlantic Ocean sea surface temperatures flip back to cooler-than-normal values – perhaps 5 or 10 years from now - the northern hemisphere sea ice areal extent should return to the normal or above normal levels seen prior to the mid 1990’s.

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