I haven’t written about polar ice conditions for a few months due to lack of time thanks to school. Hopefully my time availability moving forward will be high enough to keep this series going.
The state of global polar sea ice area in early December 2011 has temporarily returned to near climatologically normal conditions (1979-2009). Arctic sea ice has recovered very quickly after starting the freeze season slowly and Antarctic sea ice is benefiting from weather conditions preventing extensive melt at the edges in much the same way as it did last year at the same time. Since my last post (covering August conditions), polar sea ice has generally recovered from an extensive deficit of negative 2 million sq. km. The long time that sea ice area spent near this dramatic condition is unprecedented in the modern era. Poor conditions established this development across the Arctic this year.
According to the NSIDC, weather conditions this fall were slightly less conducive for Arctic sea ice melt than was the case in 2007, when the record low extent was recorded. As such, 2011′s extent was the 2nd lowest on record. Specifically, Arctic sea ice extent measured on 4.33 million sq. km. on September 9th. That was only 160,000 sq. km. more than the 2007 record low extent (about 3.7% of the minimum extent measured this year, a very small difference by comparison). For additional perspective, 2011′s minimum was 2.38 million sq. km. less than the 1979-2000 average yearly minimum. My prediction that 2011 wouldn’t miss 2007′s record by much unfortunately turned out to be true. One reason 2011′s minimum didn’t set a record was because the dipole anomaly didn’t set up in the same way or with the same intensity as 2007′s. We can’t count on these types of weather variations to disallow record lows in the future, of course. Another reason was the difference in ice motion: sea ice was likelier to remain in the Arctic in 2011 than in 2007.
Since September’s record low, Arctic sea ice has refrozen rather rapidly. September’s average sea ice extent was 4.61 million sq. km. (vs. 7.04 million sq. km. average). October’s average sea ice extent was 7.10 million sq. km. (vs. 9.29 million sq. km. normally). November’s average was 10.01 million sq. km. (vs. 11.31 million sq. km.). During the fall, sea ice extent remained near record lows set per month in years past (2007 & 2010).
In terms of longer, climatological trends, Arctic sea ice extent in September has decreased by -12% per decade; in October has decreased by -6.6% per decade; in November by -4.7% per decade. These rates are more negative this year than the previous year (a trend that has continued). These rates also use 1979-2000 as the climatological normal. There is no reason to expect these rates to change significantly any time soon. Additional low ice seasons will continue. The specific value for any given month during any given year is, of course, influenced by local weather conditions. But it becomes clearer every year that a new normal is being established in the Arctic. 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 September 10, 2011:
Figure 1 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20110910.
Compare this with August 7th’s satellite representation, also centered on the North Pole:
Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20110807.
Compare both of these with December 12th’s satellite representation (note that the AMRS-E instrument failed during early October; replacement data is available at a lower resolution):
Figure 3 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20111212.
There is more ice at this time of year in the Bering Sea and Hudson Sea than there were last year. There is missing ice north of Scandinavia – this is the result of anomalously warm conditions in that region during the past month or so.
Overall, the health of the remaining ice pack is not healthy, as the following graphs of Arctic ice volume from the end of August and November demonstrate:
Within the past month, the magnitude of ice volume anomaly grew less severe, but remains in the 2nd standard deviation from the median. Just like the sea ice extent has a negative trend, the sea ice volume is decreasing by 2900 +/-1000 cubic kilometers per decade. The volume anomaly spent a substantial amount of time beneath the 2nd st. dev. value this year, just as it did last year. The declining trend in volume ensures that future years will witness additional low areal extents.
Switching back from volume to area, take a look at September’s and December’s areal extent time series data:
Figure 6 – NSIDC Arctic sea ice extent time series through early September 2011.
Figure 7 – NSIDC Arctic sea ice extent time series through early December 2011.
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from September 10th:
Figure 8 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20110910.
Compare that graphic with the same view from December 12th (again, the AMSR-E instrument failed in October and these data are what everybody is currently working with):
Figure 9 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20111212.
Ice loss is easily visible around the continent. High ice concentrations remain well into the austral spring east of the Antarctic Peninsula (the land mass that “points” to South America).
Here is the Antarctic sea ice extent time series from September:
Figure 10 – NSIDC Antarctic sea ice extent time series through early September 2011.
For comparison, here is the same data series from December:
Figure 11 – NSIDC Antarctic sea ice extent time series through early December 2011.
You can see how recent weather conditions have slowed the rate of ice melt in the past few weeks. As weather conditions are highly variable from week to week, I expect the rate of melt to increase again soon: the +/- 2 standard deviation envelope is close to the average, as shown in Figure 11. Conditions were different in the early austral spring between 2010 and 2011. They are now much more similar in value.
The biggest reason for the different trends seen in Arctic and Antarctic data? It’s the so-called ozone hole. One project I did this semester was a literature review on the mechanisms and projections of ozone loss in the stratosphere. I will post most of that material on this blog after I make some adjustments. Put simply, ozone absorbs UV radiation (high energy) and re-radiates that energy as heat into the stratospheric air. As CFCs and other compounds have introduced halogens to the stratosphere and as UV radiation has released reactive forms of those halogens, ozone loss has occurred. As ozone concentrations decrease, less heat is re-radiated to the stratosphere. Colder air has therefore been present over Antarctica than otherwise would be the case. Greenhouse gases have reinforced this process. As CFC levels decrease in the future, however, stratospheric and columnar warming should occur. After a few more decades, global warming will have more influence over Antarctica and we will see how sea- and land-based ice is then affected.
You can find NSIDC’s December report here.
Cross-posted at SquareState.