9:30 AM | Global sea ice fights its way back to near normal after sharp drop earlier this year

Overview

Strong El Nino conditions continue to exist in the tropical Pacific Ocean as we approach the end of 2015 and this natural oceanic phenomenon ranks as one of the three strongest during the past 50 years.  In fact, this El Nino (warmer-than-normal sea surface temperatures) is likely near its peak intensity level and it has already had major ramifications around the world.  For example, global temperatures have spiked to well above-normal levels and this temperature pattern is likely to continue well into 2016.  By late 2016, however, it is looking more and more likely that El Nino will completely reverse into La Nina (colder-than-normal) conditions and – if history is any guide - global temperatures are then likely to drop sharply. 

In addition to its impact on global temperatures, the on-going strong El Nino event in the tropical Pacific Ocean has no doubt played some role in the sharp drop of global sea ice extent in recent months despite the fact that it is far removed from the polar regions.  However, as we approach the end of the year - and despite the continuing strong El Nino event - global sea ice has actually fought its way back to near-normal levels – much as it was during the past couple of years.

red line represents global sea ice areal extent compared to the 1979-2008 normal as represented by the “zero” line; data courtesy University of Illinois "cryosphere"; NOAA/NCEP Snow and Ice Data Center

Southern Hemisphere

After soaring to near record high levels during the past couple of years, sea ice in the Southern Hemisphere dropped sharply recently in areal extent from way above-normal amounts to below-normal levels.  That drop to below-normal, however, has not lasted too long.  In the past several weeks, sea ice has actually increased in areas surrounding the continent of Antarctica relative-to-normal and it is now once again running at above-normal levels (plot below), but not nearly as high as it was about one year ago.  Southern hemisphere sea ice recently stayed above-normal for a period of more than three years, from 2012 to 2015. This is something that had never happened before during the satellite period dating back to 1979. 

Southern Hemisphere sea ice anomaly since 1979; data courtesy University of Illinois “cryosphere”

Northern Hemisphere

The northern hemisphere sea ice areal extent is still below-normal relative to all years going back to 1979 although it is well above the lowest point set during 2012 - and even above levels seen earlier this year. The northern hemisphere sea ice areal extent is currently 742,000 square kilometers below the mean using the base period of 1979-2008 for comparison (plot below). The northern hemisphere sea ice areal extent has leveled off in the past 10 years or so at below-normal levels after dropping consistently from the mid 1990’s to the middle of the last decade. In the time period before the mid 1990’s, the sea ice areal extent was generally above-normal dating back to 1979. 

Northern Hemisphere sea ice anomaly since 1979; data courtesy University of Illinois “cryosphere”

The directional shift in the sea ice areal extent 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, Atlantic Ocean sea surface temperature anomalies play a critical role in the overall northern hemisphere sea ice areal extent. The AMO index flipped in phase during the mid-1990’s from negative (cold) to positive (warm) and the sea ice areal extent trendline changed direction right around that point in time.

The Atlantic Ocean is just recently showing signs of a long-term temperature phase shift back to cold and if that trend continues over the next couple of years then the northern hemisphere sea ice areal extent is quite likely to return to the same above-normal levels that were seen prior to the mid 1990’s. (Click here for more information on the potential significant long-term temperature phase shift in the Atlantic Ocean: http://vencoreweather.com/2015/03/22/1230-pm-the-atlantic-ocean-is-showing-signs-of-a-possible-significant-long-term-shift-in-temperatures-from-warm-to-cold/). 

In fact, the northern hemisphere sea ice has actually shown great resiliency in recent years and has rebounded to the highest levels seen during the past ten years according to recent data from the Danish Meteorological Institute (plot below, http://ocean.dmi.dk/arctic/old_icecover.uk.php ).

Northern hemisphere sea ice extent for 2015 (black line); Note - the sea ice extent here is calculated with the coastal zones masked out.

Meteorologist Paul Dorian

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