Arctic Sea Ice: Some History Since 2011
I had written a series of diaries in 2009-2011 on the state of Arctic Sea Ice. Those years were marked by lower than normal summer sea ice extent; all below the average extent for the decade of the 2000s. The following year, 2012, had the lowest minimum sea ice extent in the modern record; 18% below the previous one set in 2007. A large reason was a major storm in August, breaking up sea ice and transporting it to lower latitudes.
So what has happened since 2012? Here’s a graphic showing the Arctic Sea Ice extent each year since then, up through yesterday, 27 July 2021.
Sea ice extent since 2012 has at all seasons both been below the 1981-2010 median (dark gray), but below the 10th percentile from that 30-year period as well. In the graphic, the 10th percentile is shown by the lower bound of the light-colored shading. It’s fair to say that the trends observed since the 1990s have continued unabated, though with some annual variation. Note that the second lowest sea ice extent in the satellite-observed record (which started in 1979) occurred last year.
The Current Snapshot
What is the state of the Arctic Sea Ice today?
Sea ice concentration
As of 27 July, sea ice concentration (%age area covered with ice) was as shown in the graphic above. White areas are solid ice. The scale on the right indicates the relative concentration as the blue colors go from pale to dark. Anywhere with less than 15% sea ice concentration is considered open water. The median (50th percentile) sea ice edge for this date over the 1981-2010 period is shown in orange.
sea ice concentration
Sea ice extent is less than normal pretty much everywhere in the Arctic Ocean except for north of Greenland and the Arctic Archipelago. This is the home of the ice that persists from year to year, surviving the summer melt season. Such ice covers a much smaller area than it has in the past.
The graphic below focuses on the time series since 1 April.
The 2021 time series has tracked very closely to 2012 since late May. While this sounds ominous, recall that the current extent lies somewhere in the middle of the 2012-2020 distribution, and that August storm in 2012 helped to drive sea ice extent to the lowest observed minimum.
sea ice volume
When considering the Arctic Ocean surface energy balance and its past, present, and potential future effect on sea ice loss, sea ice volume is far better to use than sea ice concentration or extent. The graphic below shows a reconstruction of its time series since 1979, courtesy of the University of Washington’s Polar Science Center.
The story told is similar to Arctic Sea Ice extent: increasingly negative volume anomalies with interannual variability and periodic accelerations and pauses. Since 2012, a brief recovery took place up to 2016, followed by a decline and then a quasi-steady state.
Any Projections/Forecasts?
Minimum sea ice extent forecasts are made by many research and operational forecast centers. These centers use a variety of different methods, including heuristic (best guesses), statistical (based on past data), and dynamical (physically realistic) models. Luckily, the Arctic Research Consortium of the United States solicits these forecasts on a monthly basis, and then summarizes them on its Sea Ice Prediction Network webpage. The forecasts issued by the contributors (41 in all) are shown below. I’ve added the record 2012 minimum as a vertical gray line for reference. Note that the different colors indicate forecast methodology as indicated by the legend on the right.
The different methods combined together can be considered an ensemble of forecasts. Ensemble forecasts are used for many weather and climate problems, including estimating the impact of global warming using different CO2 scenarios and different climate models.
Phenomena that impact Arctic Sea Ice extent (and volume) are:
- The amount of direct sunlight reaching the ice surface
- The amount of snow lying on the ice
- The sea water temperature beneath the ice.
- Ocean currents advecting warm water into the Arctic Ocean
- Cyclonic storms that can break up the ice pack if strong enough
- Ice age and thickness.
Of all the methods, dynamic models represent most or all of these processes in their sea ice extent forecasts.
We’ll revisit this forecast after the September sea ice minimum to see how good the forecast was.