The state of global polar sea ice area in early January 2012 has convincingly returned to climatologically normal conditions (1979-2009). Arctic sea ice has recovered very quickly after a late start to the freeze season and a late-season slowdown due to certain atmospheric and oceanographic conditions; Antarctic sea ice has melted only slightly more slowly than is normal during the austral summer. Put another way, polar sea ice has recovered from an extensive deficit of -2 million sq. km. area a couple of months ago to zero anomaly today. That said, sea ice area spent an unprecedented length of time near the -2 million sq. km. deficit in the modern era. Generally poor environmental conditions established and maintained this condition, predominantly across the Arctic this year.
According to the NSIDC, weather conditions this winter were slightly less conducive for Arctic sea ice freezing on the Atlantic side of the Arctic while conditions were more conducive for freezing on the Pacific side. As such, February′s extent was the 5th lowest on record. Additionally, Arctic sea ice extent on in February averaged just 14.56 million sq. km. Sea ice extent was well below average in the Barents Sea due to temperatures that were 7-14°F above normal! The Bering and Baffin Seas meanwhile saw ice extent and ice growth, respectively, above normal during the month.
During February, Arctic sea ice refroze more rapidly than is the case for most Februaries. February’s sea ice extent increased by 956,000 sq. km., almost 2X the normal rate – largely due to previously low ice extent conditions in the Baffin Sea. Specific conditions around the Arctic Ocean were highly influenced by the positive phase of the North Atlantic Oscillation.
In terms of longer, climatological trends, Arctic sea ice extent in February has decreased by -3% per decade. This rate is lowest in the winter months than the late summer 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. Additional low ice seasons will continue. Some years will see less decline than other years – 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 a new normal is being established 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 7, 2012:
Figure 1 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120107.
Compare this with March 9th’s satellite representation, also centered on the North Pole:
Figure 2 – UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120309.
Once Hudson Bay finally froze over around the time of the New Year, ice extent grew toward the Atlantic Ocean. The sea ice in the Bering Sea, as mentioned above, formed more quickly than is normal. What is largely still missing is the sea ice north of Scandinavia. This is the result of anomalously warm waters from the Gulf Stream being drawn further north than is normal. This is due to the positive AO & NAO indices during this winter. As a side note, this phenomenon combined with the moderate La Nina in the Pacific Ocean has led to Dec-Mar being a warm and dry month for most of the U.S. so far
Overall, the health of the remaining ice pack is not healthy, as the following graph of Arctic ice volume from the end of February demonstrates:
As the graph shows, volume hit a record minimum earlier in 2011 before returning to the -2 standard deviation envelope. I know most folks don’t have a very good 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 2 of them occurring in 2 subsequent years under normal conditions are very, very remote. Hence my assessment that “normal” conditions in the Arctic are shifting from what they were in the past few centuries.
Switching back from volume to area, take a look at February’s areal extent time series data:
Figure 4 – NSIDC Arctic sea ice extent time series through early March 2012.
As you can see, the sea ice extent has spent all of the fall and early winter well outside of the -2 standard deviation envelope, just as it has for 5 winters in a row. It cannot be stated otherwise: these conditions are not indicative of a healthy system. This winter brought something new that the past few winters did not, however a return of ice extent to within the -2 standard deviation envelope. The reason for this is a shift in wind conditions: speed and direction both changed from early winter through this last month. Those winds pushed sea ice apart instead of piling it up. The advantage: ice extent increased, as seen in Figure 4. The disadvantage: ice volume stopped growing, as seen in Figure 3. The effect on this September’s minimum extent will indicate how helpful the early season winds were in building sea ice that doesn’t melt every year back up.
Occasionally, I also like to include a supplemental time series graph that the NSIDC report contains. Here is this month’s supplemental graph:
Figure 5 – NSIDC Arctic sea ice extent time series through early March 2012.
This graph contains all of the same data as the previous graph and adds time series from 4 of the previous 5 winters. As you can see, extent varies during the same month from year to year. The recent surge in extent, caused by a change in wind direction and speed, has brought Arctic ice extent up to ~15 million sq. km., which is challenging the highest extent in the most recent 6 winters. The maximum 2007 and 2011 ice extent didn’t come close to 15 million sq. km. while 2010 achieved approximately the same value almost a full month later. Despite these differences in subsequent years, the minimum ice extent values were quite similar: at or near the record low set in 2007. Will fall 2012 be any different?
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from January 7th:
Figure 6 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20120107.
Compare that graphic with the same view from March 9th:
Figure 7 – UIUC Polar Research Group‘s Southern Hemispheric ice concentration from 20120309.
Ice loss is less easily visible around the continent in these two images than they were between previous months. High ice concentrations remain well into the austral summer (nearly fall) east of the Antarctic Peninsula (the land mass that “points” to South America). Conditions of Antarctic sea ice remain good this year. As a reminder, this is largely and somewhat confusingly due to the ozone depletion that took place over the southern continent. This depletion has caused the southern polar stratosphere to be colder than it otherwise would be, reinforcing the polar vortex over the Antarctic Circle. That 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. For now, we should perhaps consider the relative fortune the lack of ozone has produced.
Here is the Antarctic sea ice extent time series from February:
Figure 8 – NSIDC Antarctic sea ice extent time series through early March 2012.
Melt rates have been at or near normal throughout the austral summer this year. Year-to-year variation is also present in this graph, which includes the previous winter’s extent as a comparison. At this point, no news is good news. The Arctic is providing more than enough excitement for the time being.
You can find NSIDC’s January report here.
Cross-posted at SquareState.