Global polar sea ice area in early January 2013 remains below climatological normal conditions (1979-2009), but has improved in the past month. Antarctic sea ice loss is occurring at a climatological normal rate. Arctic sea ice gain is slightly more rapid than normal, but we should expect this given the record low extent that occurred in September 2012. Polar sea ice recovered from an extensive deficit of -2.5 million sq. km. area late last year to a -500,000 sq. km. anomaly within the last week.
In March-April 2012, global sea ice area was above normal, but sea ice area anomaly quickly turned negative and then spent an unprecedented length of time near the -2 million sq. km. deficit in the modern era in 2012. Generally poor environmental conditions (warm surface temperatures and certain wind patterns) established and maintained this condition, predominantly across the Arctic last year. For the third time in modern history, the minimum global sea ice area fell below 17.5 million sq. km. and for the fourth time in modern history, the anomalous global sea ice area fell below -2 million sq. km. This is a significant development given that Antarctic sea ice area has been slightly above average during the past few years. This means that the global anomaly is almost entirely due to worsening Arctic ice conditions.
The rapid ice melt and record-setting area and extent values that occurred in 2012 are the top weather/climate story for 2012, in my opinion. I think we have clearly seen a switch to new conditions in the Arctic. Whether these events will occur in similar magnitude or are merely transitory as the Arctic continues to move to a new stable state that the climate will not achieve for years or decades remains to be seen. The problem is we don’t know all of the ramifications of moving toward or achieving that new state. Additionally, I don’t think we want to know.
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. Similar conditions occurred during the past six years. Sea ice creation during December measured 2.33 million sq. km. Despite this rather rapid growth, December?s extent remained far below average for the month. Instead of measuring near 13.36 million sq. km., December 2012?s extent was only 12.2 million sq. km., a 1.16 million sq. km. difference! The Barents and Kara Seas remained ice-free, which is a very unusual condition for them in December. Recent ice growth in the Seas has slightly alleviated this state, but this is happening very late in the season. The Bering Sea, which saw ice extent growth due to anomalous northerly winds in 2011-2012, saw similar conditions in December 2012. This has caused anomalously high ice extent in the Bering Sea. Temperatures over the Barents and Kara Seas were 5-9°F above average while temperatures over Alaska were 4-13°F below average. The reason for this is another negative phase of the Arctic Oscillation, which allows cold Arctic air to move southward. This allows warm sub-arctic air to move north.
In terms of longer, climatological trends, Arctic sea ice extent in December has decreased by 3.5% 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 (like this past year) – 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 [cont’d.]