Global polar sea ice area in early February 2013 mimics climatological normal conditions (1979-2009), after improvement in the past month. Antarctic sea ice loss is occurring slower than the climatological normal rate. Arctic sea ice gain is more rapid than normal. Polar sea ice recovered from an extensive deficit of -2.5 million sq. km. area late last year to near-zero anomaly within the last week.
According to the NSIDC, weather conditions once again caused less freezing to occur on the Atlantic side of the Arctic Ocean and more freezing on the Pacific side than normal. Similar conditions occurred during the past six boreal winters. Sea ice creation during January measured 1.36 million sq. km. Despite this rather rapid growth, January′s extent remained well below average for the month. Instead of measuring near 14.84 million sq. km., January 2013′s extent was only 13.78 million sq. km., a 1.06 million sq. km. difference! The Barents Sea recorded lower than average sea ice, which is an unusual condition for January. Kara Sea ice recovered from low extent the past couple of months. The Bering Sea, which saw ice extent growth due to anomalous northerly winds in 2011-2012, saw similar conditions in December 2012 and January 2013. This has caused anomalously high ice extent in the Bering Sea. Previously this winter, a negative phase of the Arctic Oscillation allowed cold Arctic air to move far southward and brought warmer than normal air to move north over parts of the Arctic. The AO has returned to a more neutral phase in the past month, which has kept Arctic air closer to where it normally is this time of year.
In terms of longer, climatological trends, Arctic sea ice extent in January has decreased by 3.2% per decade. This rate is closest to zero in the spring months and furthest from zero in late summer/early fall months. Note that this rate also uses 1979-2000 as the climatological normal. There is no reason to expect this rate to change significantly (more or less negative) any time soon, but increasingly negative rates are likely in the foreseeable future. Additional low ice seasons will continue. Some years will see less decline than other years (e.g., 2011) – but the multi-decadal trend is clear: negative. The specific value for any given month during any given year is, of course, influenced by local and temporary weather conditions. But it has become clearer every year that humans have established a new climatological normal in the Arctic with respect to sea ice. This new normal will continue to have far-reaching implications on the weather in the mid-latitudes, where most people live.
Arctic Pictures and Graphs
The following graphic is a satellite representation of Arctic ice as of January 9, 2013:
Figure 1 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20130109.
Here is the similar image from February 11th 2013:
Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20130211.
The lack of sea ice in the Barents Sea (north of Europe) is problematic because wind and ocean currents typically pile sea ice up on the Atlantic side of the Arctic. Sea ice presence in the Bering Sea (between Alaska and Russia) does not alleviate this problem because currents take ice from that area and transport it into the Arctic. That sea ice will be among the first to melt completely come spring. With sea ice missing on the Atlantic side, currents will more easily transport Arctic sea ice to southern latitudes where it melts.
Overall, the health of the ice pack is not healthy, as the following graph of Arctic ice volume from the end of January demonstrates:
Figure 3 – PIOMAS Arctic sea ice volume time series through January 2013.
As the graph shows, volume (length*width*height) hit another record minimum in June 2012. Moreover, the volume remains far from normal since it just returned to the -2 standard deviation envelope (light gray). I understand that most readers don’t have an excellent handle on statistics, but conditions between -1 and -2 standard deviations are rare and conditions outside the -2 standard deviation threshold (see the line below the shaded area on the graph above) are incredibly rare: the chances of 3 of them occurring in 3 subsequent years under normal conditions are extraordinarily low (you have a better chance of winning the Powerball than this). Hence my assessment that “normal” conditions in the Arctic are shifting from what they were in the past few centuries; a new normal is developing. Note further that the ice volume anomaly returned to near the -1 standard deviation envelope in early 2011, early 2012, and now early 2013. In each of the previous two years, volume fell rapidly outside of the -2 standard deviation area with the return of summer. That means that natural conditions are not the likely cause; rather, another cause is much more likely to be responsible for this behavior: human influence.
Arctic Sea Ice Extent
Take a look at January’s areal extent time series data:
Figure 4 – NSIDC Arctic sea ice extent time series through early February 2013.
As you can see, the extent (light blue line) grew rapidly in November but still remained at historically low levels through the winter. The extent remained well below average values (thick gray line) throughout the fall and early winter. The time series of sea ice extent for previous low years is also shown on this graph. In this month’s version, NSIDC also plotted the previous four years’ data. You can see the effect of the wintertime conditions that I described above: the difference between a year’s extent and the average value in January or February is smaller than the difference in October. This leads us to examine the differences between the historical mean, the negative two standard deviation (light gray) below that mean, and the 2012-2013 time series.
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from January 9, 2013:
Figure 5– UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20130109.
And here is the corresponding graphic from February 11th:
Figure 6 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20130211.
Ice loss is easily visible around the continent. There is slightly more Antarctic sea ice today than there normally is on this date in the year. The reason for this is the extra ice in the Weddell Sea (east of the Antarctic Peninsula that juts up toward South America). This ice exists this winter due to an anomalous atmospheric circulation pattern: persistent high pressure west of the Weddell sea pushed sea ice north. The same winds that pushed the sea ice north also moved cold Antarctic air over the Sea, which has kept ice melt rate well below normal. A similar mechanism helped sea ice form in the Bering Sea so far this winter.
As a reminder, the difference between long-term Arctic ice loss and relative lack of Antarctic ice loss is largely and somewhat confusingly due to the ozone depletion that took place over the southern continent in the 20th century. This depletion has caused a colder southern polar stratosphere than it otherwise would be, reinforcing the polar vortex over the Antarctic Circle. This is almost exactly the opposite dynamical condition than exists over the Arctic with the negative phase of the Arctic Oscillation. The southern polar vortex has helped keep cold, stormy weather in place over Antarctica that might not otherwise would have occurred to the same extent and intensity. As the “ozone hole” continues to recover during this century, the effects of global warming will become more clear in this region, especially if ocean warming continues to melt sea-based Antarctic ice from below (subs. req’d). For now, we should perhaps consider the lack of global warming signal due to lack of ozone as relatively fortunate. In the next few decades, we will have more than enough to contend with from melting on Greenland. Were we to face melting West Antarctic Ice Sheet at the same time, we would have to allocate many more resources. Of course, in a few decades, we’re likely to face just such a situation.
Finally, here is the Antarctic sea ice extent time series from February 11th:
Figure 7 – NSIDC Antarctic sea ice extent time series through early February 2013.
Given the lack of climate policy development to date, Arctic conditions will likely continue to deteriorate for the foreseeable future. The Arctic Ocean will soak up additional energy from the Sun due to lack of reflective sea ice. Additional energy in the climate system creates cascading effects through the system. The energy pushes the Arctic Oscillation to a negative phase, which allows anomalously cold air to pour south over Northern Hemisphere land masses while warm air moves over the Arctic. This impacts weather patterns throughout the year.
More worrisome for long-term concerns is the heat that impacts land-based ice. As glaciers and ice sheets melt, sea-level rise occurs. Beyond the increasing rate of sea-level rise, storms have more water to push onshore as they move along coastlines. We can continue to react to these developments as we’ve mostly done so far. Or we can be proactive, minimize future global effects, and reduce societal costs. The choice remains ours.