The state of global polar sea ice area at the beginning of 2011 continues the trend present throughout most of 2010: well below climatological conditions (1979-2009). Sea ice in the Arctic continues to track far below average while Antarctic sea ice has tracked closer to average from above average the past couple of months. Overall, the rate at which Arctic sea ice is refreezing and Antarctic ice is melting is not out of the ordinary. The locations where freezing and melting is occurring is once again news this month. Global sea ice is rapidly decreasing, as is normal for this time of year due to Antarctic environmental conditions. The value of global sea ice area has already fallen below the average level of 16 million sq. km. The yearly absolute minimum should occur within the next month or so, at which time we’ll be able to determine whether 2011′s minimum is more like 2005, 2009 and 2010 (~15 million sq. km.) or whether 2011′s minimum is more like 2006 and 2007 (~14.5 million sq. km.).
The rate of freezing of Arctic sea ice continued to slow down from November to December. The ice extent averaged over December 2010 was the lowest on record: 12 million sq. km., which was 270,000 sq. km. below the previous record low set in 2006. The presence of relatively warm pockets of water in the region, combined with local weather patterns present during November, helped push the extent to a record low.
In December, the ice extent was about 1 million sq. km. less every day than the normal value. This was the first time on record that the extent was so low for so long during the last calendar month of the year. The extent was ~200,000 sq. km. lower than during the same period in 2009 and ~500,000 sq. km lower than during the same period in 2008. Recall that the ice extent was anomalously low for the longest period of time (5 months) and the 2nd lowest overall extent on record (behind 2007) in 2010. The last time the ice extent was at zero anomaly was way back in December 2004. The last time the ice extent spent more than a day or two above the zero anomaly line was back in early 2003. The change in December ice extent has been measured at -3.5% per decade by the NSIDC. It should be noted that for the first 16 years of that record, the extent didn’t have a significant positive or negative trend. It is only since the early 1990s that a noticeable trend has developed. I’ve written many times now that the Arctic appears to have entered a new regime. These kinds of anomalous conditions characterize that new regime. I don’t definitively know what a -1.181 million sq. km. ice extent in early January means for September ice extent. I am not confident that it means September ice conditions will return to normal.
More important to polar climate processes than areal extent, however, is the volume of ice. Arctic ice volume has been decreasing for decades, but has worsened considerably in the past 5 years. After setting a record low earlier this year, ice volume rebounded somewhat so that it was back within the -2 standard deviation envelope. In December, the volume looks to have stabilized near -8 million cubic km. We should all hope that the volume stays at or near this level instead of plummeting to new record lows as it did in 2010.
Arctic Pictures and Graphs
Here is a satellite representation of Arctic sea ice conditions from January 6th centered on the North Pole:
Compare these with December 5th’s satellite representation, centered on the Hudson Bay:
The white oval in the January map highlights an area where sea ice remains missing weeks to months after it normally forms. I wrote last month that the Hudson Bay was normally half covered with ice by the end of November. It should ice over the its entire surface by now. But you can see that the Bay still doesn’t have ice cover near its eastern shoreline. Why is this? Near-surface air temperatures in this region were 4-8F warmer than normal in December. It has been warm enough to stave off ice formation for weeks to months later than usual. Also in the white oval is the west coast of Greenland and Baffin Island. Want some really frightening news? These regions witnessed near-surface air temperatures that were 8-12F warmer than normal. As a result, these regions remain ice-free in the middle of winter. That’s not a good sign. Neither are the warmer sea surface temperatures in the North Atlantic and off the west coast of Greenland.
One cause of these conditions is the Arctic Oscillation, which has allowed cold Arctic air to move much further south than normal, hence the rough winters that the eastern U.S. and Europe are facing. The Arctic Oscillation Index was slightly positive in the beginning of November, but transitioned to negative in the second half of November before returning to near zero by the beginning of December and finally turning very negative again in mid-December. This is the third winter in a row that the AO Index was extremely negative. The NSIDC notes that
Starting in the 1970s, however, the oscillation has tended to stay in the positive phase, causing lower than normal arctic air pressure and higher than normal temperatures in much of the United States and northern Eurasia.
So the most recent winters in some areas are indeed out of the “normal” realm that many people grew up experiencing.
Here is the time series graph of Arctic sea ice extent with the +/- 2 standard deviations as a light-gray envelope around the climatological average through January 6th:
The red ovals highlight important chances in Arctic sea ice extent. Ice extent actually declined during those two periods – the first in the middle of December and another one in the first week of January. This has occurred in the past, but it is very rare for the ice extent to shrink during the middle of the winter. After declining in December, the Arctic sea ice extent was the lowest on record for those calendar days. As you can see from the above time series, the extent continues to set calendar-day record lows.
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from January 6th:
For comparison purposes, here is the similar picture from December 5th:
I pointed out the areas highlighted by white ovals in the December picture as “ice-free ocean close to a continental land mass surrounded by solid sea ice”. Sea ice near those areas continued to melt from the continent out, but ocean currents and weather patterns also melted neighboring ice from the sea in. Above-average near-surface temperatures near the areas in the white ovals continued through December, helping to melt the ice in this fashion. You can see that the sea ice off Eastern Antarctica (near the bottom white oval) almost completely melted away during December. That is a fairly common occurrence. Sea ice off Western Antarctica has been able to stay together a little while longer. Massive fields of sea ice in rather poor condition can still be found in this area (blue colors indicating low sea ice concentration). Perhaps of more interest is the sea ice that is still in good condition off the east coast of the Antarctic peninsula (the rather skinny piece of land sticking out into the ocean) and the sea ice hugging the coast to the west of the Antarctic peninsula. These areas experienced cooler than normal conditions (surface temperature) during December. If local temperatures continue to stay below normal the rest of the austral summer, the sea ice could hang around for another season.
Here is the time series graph of Antarctic sea ice extent with the +/- 2 standard deviations in light gray and the climatological mean in dark gray through the 6th:
Antarctic sea ice in late 2010 declined from its above-average extent witnessed during October and November. The extent is now near the long-term average value of 5-6 million sq. km. The extent heading into 2011 is slightly lower than the extent heading into 2010. The NSIDC had this to say about Antarctic conditions:
The high ice extent around Antarctica appears to relate to a persistently positive phase of the Southern Annular Mode—an Antarctic counterpart to the Arctic Oscillation—and to the mild La Niña conditions in the Pacific.
For the time being, at least, seasonal forcings are the primary driver of Antarctic sea ice. Conditions in the Southern Hemisphere certainly are not as anomalous as conditions in the Northern Hemisphere.
You can find the NSIDC’s January report here. The page is dynamic, so if you’re reading this after January 2011, that month’s report will show up first. If that’s the case, you can look for any report in their archive on the top pull-down tab on the right-hand side of the page.
Cross-posted at SquareState.