There has been talk in the climate community over the past several years that the Arctic Ocean would be nearly ice-free by now, but sea ice in the Arctic region has actually shown great resiliency. Sea ice covers about 7% of the Earth’s surface and about 12% of the world’s oceans and forms mainly in the Earth’s polar regions (i.e., in the Northern Hemisphere’s Arctic Ocean and in the sea area around the Southern Hemisphere’s continent of Antarctica). While the Southern Hemisphere sea ice extent has been running consistently at above-normal levels in the past few years and often at record highs, the Northern Hemisphere has generally been at below-normal amounts. In this same time period; however, sea ice in the Arctic region has shown a great ability to recover which has confounded many global climate modelers and it has actually been in a general upward trend since reaching a low point in 2012 (example journal article on measured versus modeled discrepancies in sea ice data: http://www.hindawi.com/journals/amete/2015/481834/). Furthermore, in recent months the northern Atlantic Ocean has begun to show signs of a potential long-term temperature phase shift from warm-to-cold and this could very well lead to a significant further rebound in Arctic sea ice – perhaps eventually to the above-normal levels seen during the last cold phase.
[Sea surface temperature anomalies as of July 27, 2015; courtesy NOAA]
North Atlantic Sea Surface Temperature (SST) Change
The northern Atlantic Ocean switched sea surface temperature phases from cold-to-warm back in the mid 1990’s and this shift was directly correlated with the flipping of Arctic sea ice extent from above-normal to below-normal and it has generally been below-normal since that point in time. The sea surface temperature phase in the northern Atlantic Ocean is tracked by meteorologists with the Atlantic Multidecadal Oscillation (AMO) index and in recent months this number has been bouncing back-and-forth between negative (cold) and positive (warm) values suggesting a possible long-term phase change may indeed be taking place. An area of colder-than-normal sea surface temperatures (blue region in circled area) has expanded significantly in recent months across the northern Atlantic Ocean and temperatures in the Arctic region have run at normal-to-slightly below-normal levels (plot below, circled area; green line represents normal). [For more information on the possible Atlantic Ocean temperature phase shift: 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/].
Daily mean temperature and climate north of the 80th northern parallel, as a function of the day of year. Source: Danish Meteorological Institute (DMI) – Centre for Ocean and Ice; http://ocean.dmi.dk/arctic/meant80n.uk.php
Significant improvement in Arctic sea ice extent since 2012
One of the lowest points with respect to Arctic sea ice took place in the year 2012. During that year, Arctic sea ice bottomed out during the peak of the melting season (late summer) to levels not seen before in the satellite era (since 1979). Recent reports based on satellite observations, however, indicate the Arctic sea ice recovered noticeably in 2013 increasing by almost one-third – albeit from very low levels. For the last couple of months, Arctic sea ice has been running at levels higher than those seen during the past three years – although still at below-normal levels – and it has been running safely above the low point year of 2012 (“black” line in circled area below).
Source: Danish Meteorological Institute (DMI) – Centre for Ocean and Ice (sea ice extent 15% or greater)
Upward trend in Arctic sea ice volume since 2012
In addition to sea ice extent, an important climate indicator to monitor is sea ice volume as it depends on both ice thickness and extent. Arctic sea ice volume cannot currently be observed on a continuous basis as observations from satellites, submarines and field measurements are all limited in space and time. As a result, one of the best ways to estimate sea ice volume is through the usage of numerical models which utilize all available observations. One such computer model from the University of Washington is called the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS, Zhang and Rothrock, 2003) and it is showing an upward trend in Arctic sea ice volume since the low point was reached in 2012 following a long downtrend (circled area below). We’ll continue to monitor changes in coming months here at VencoreWeather.com with respect to the Arctic sea ice to see if the recovery from low levels continues and we’ll also watch the overall situation in the southern hemisphere.
Arctic sea ice volume from the University of Washington’s PIOMAS numerical model (Note – this model output data is updated on a monthly basis, details on the PIOMAS model are available at http://psc.apl.washington.edu/research/projects/arctic-sea-ice-volume-anomaly.