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Weather forecasting and analysis, space and historic events, climate information

12:30 PM | Southern hemisphere sea ice areal extent reaches record high in satellite era; northern hemisphere continues at well below normal levels, but above the low point set two years ago

Paul Dorian

antarctica[Yellow line represents 2014 southern hemisphere sea ice areal extent; courtesy University of Illinois "cryosphere" and NOAA/NCEP]

Discussion

Overall Summary The amazing recent expansion of Southern Hemisphere sea ice areal extent has continued and it has just reached an all-time high in the satellite data era which began 35 years ago in 1979 (above). This is the time of year when the southern hemisphere usually reaches its highest extent for the year (i.e., just ended their winter season) and the high for this year has also surpassed the all-time high during the past 35 years of record-keeping. The northern hemisphere sea ice areal extent – now near the low point of the year (i.e., just ended their summer season) - continues at well below normal levels, but it is above levels seen two years ago which were the lowest minimum amounts recorded since 1979. Overall, given the recent surge in the southern hemisphere to record levels, the global sea ice areal extent has spiked into “above-normal” territory (below).

global_sea_ice [red line represents 2014 global sea ice areal extent relative to normal at zero line; courtesy University of Illinois "cryosphere" and NOAA/NCEP]

Southern Hemisphere Sea Ice The remarkable period of increasing sea ice areal extent in this part of the world has actually been occurring for the past few years with only a few brief exceptions to that overall upward trend. Back in 2011, the southern hemisphere sea ice areal extent was at below-normal levels, but it is currently running nearly 1.7 million square kilometers above the 1979-2008 mean (courtesy University of Illinois "cryosphere" web site with data originating from NOAA/NCEP Snow and Ice Data Center).

Northern Hemisphere Sea Ice The northern hemisphere sea ice areal extent is still well below normal relative to all years going back to 1979 although it is noticeably above the lowest point set two years ago at this same time of year (plot below). The northern hemisphere sea ice areal extent is about 1.2 million square kilometers below normal using the base period of 1979-2008 for comparison. The northern hemisphere sea ice areal extent has generally trended lower since the mid 1990’s reaching primarily below-normal levels after the turn of the century. In the past several years, however, there has been a leveling off of that downward trend in terms of sea ice areal extent at those below-normal levels.

In the time period before the mid 1990’s, the sea ice extent was generally above-normal dating back to 1979. The directional shift in trendline that developed during the mid 1990’s in the northern hemisphere 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 areal extent and the AMO index flipped in phase during the mid 1990’s from negative (cold) to positive (warm) and the trend changed direction at that point in time. Once the northern Atlantic sea surface temperatures flip back to cooler-than-normal values – perhaps in the next few years - the northern hemisphere sea ice areal extent should return to the normal or above-normal levels seen prior to the mid 1990’s.

arctic [Yellow line represents 2014 northern hemisphere sea ice areal extent; courtesy University of Illinois "cryosphere" and NOAA/NCEP]