The state of global polar sea ice area in the middle of April 2011 remains poor: well below climatological conditions (1979-2009) continue to persist. Sea ice in the Arctic continues to track significantly below average, with the 2nd lowest readings for the month in the modern era. Antarctic sea ice has rebounded very slowly from its annual minimum extent, hovering near record low extent values during March and only recently improving in comparison to historical lows in early April. Global sea ice area has therefore remained near historical lows for an extended period of time this year. While global sea ice area has rebounded from its yearly minimum, the difference between this year and climatological conditions has been stuck below negative 1 million sq. km. for the first 3.5 months this year. Those conditions mimic the trend seen in early 2006 and 2007. 2006 saw the global area increase to normal conditions later in the year. 2007, in contrast, did not. That, of course, was the year that Arctic sea ice extent plummeted to its lowest value on record. Weather conditions in the Arctic the rest of this year will help determine whether 2011 challenges 2007 for that dubious position.
According to the National Snow and Ice Data Center, Arctic sea ice extent in March was the 2nd lowest on record. Averaged over March 2010, Arctic sea ice extent was only 14.56 million sq. km. Arctic ice in March and into early April didn’t change very much in its extent. This is definitely typical for March, but less so for April. In fact, overall conditions have held steady since mid-February. While those conditions were extremely low compared to climatological conditions in February, they were less anomalous by the middle of April. Climatologically, the extent starts to really decrease by the beginning of April, so the extent anomaly has sharply decreased in the past month from 1.1 million sq. km. below normal to “only” 574,000 sq. km. below normal now. Hopefully that translates to the lack of record low extents later this year.
The change in March ice extent has been measured at -2.7% per decade by the NSIDC. What that means is as of the end of March 2011, the Arctic has only 14.56 million sq. km. of sea ice extent, while as of the end of January1978, the Arctic had 16.49 million sq. km. of sea ice. That difference is real and it is significant.
Arctic Pictures and Graphs
I’m going to do something a little different this month and compare April’s satellite imagery of the Arctic to February’s to demonstrate the general lack of difference between the two.
Compare this with February 7th’s satellite representation, centered on the North Pole:
A couple of areas have some lower concentration of sea ice, but the general picture looks the same as it did over two months ago. One important factor in April’s conditions is the Arctic Oscillation’s return to more positive values since the beginning of the year. This has allowed colder air to remain in place over the Arctic region.
As a whole, here is what the Arctic ice extent looks like in time-series form through April 19th:
The NSIDC has included the 2007 time-series line as a useful comparative measure for this year’s extent. After trailing below 2007 conditions for the first 2 months this year, the unchanging extent since early March has meant 2011’s extent is now above 2007’s. At the end of the 2011 series, you can see that this year’s melt season might finally be in effect.
Antarctic Pictures and Graphs
Here is a satellite representation of Antarctic sea ice conditions from April 19th:
For comparison purposes, here is the similar picture from March 2nd:
Sea ice conditions have obviously increased in the last month, as they should have. To date, I haven’t seen anything regarding the health of the ice shelves ringing the continent. The longer there is no news, the better, since those shelves keep the land-based ice on land and not allowing them to escape to the sea.
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 April 19th:
Antarctic sea ice extent has remained on the low side of the climatological envelope of conditions. So far, April has seen more extensive freezing than did March. As you can see, conditions this year have been worse than conditions in 2010. Unlike the Arctic, however, a long-term trend has not been as dramatic in the Antarctic.
You can find the NSIDC’s April report here. The page is dynamic, so if you’re reading this after April 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.