The state of global polar sea ice at the beginning of October 2010 was once again very poor compared to climatological conditions (1979-2008). The Arctic ice extent was far, far below average for this time of year. The Antarctic sea ice extent wass above average, but not nearly so much as was the case in the Arctic. Unfortunately, global sea ice extent fell to ~17.5 million sq. km., something that has happened in only 2 previous Septembers: in 2007 and 2008. The Northwest Passage and the Northern Sea Route are largely free of ice, allowing the Arctic Ocean to potentially be circumnavigated.
This post will mostly concentrate on the extremely poor conditions found in the Arctic this fall. Antarctic conditions are not as extreme, largely and ironically thanks to the ozone hole over the continent which has kept stratospheric temperatures much cooler than they otherwise would be. Eventually, our forcing leading to global warming will overwhelm the ozone hole cooling effect (and the ozone hole will gradually be “healed” anyway), which will cause long-term changes to Antarctica just like the Arctic.
In September, younger ice continued to melt rapidly. Older ice ended up at historical lows, which means more summers of at least near-record low extents and additional record low ice volumes. Ice extent reached its low for the year, the third lowest in recorded history, on September 19th. 2008’s low extent was only slightly lower than 2010’s. 2007’s record low extent was still significantly lower than either 2010’s or 2008’s.
In terms of monthly averages, 2010’s September extent was 2.14 million square kilometers (830,000 square miles) below the 1979 to 2000 average, but 600,000 square kilometers (230,00 square miles) above the average for September 2007. A time series graph maintained by the University of Illinois at Urbana-Champaign’s Polar Research Group shows that 2010 was a noteworthy year for another reason: shortly after the sea ice extent anomaly nearly maxed out at 0 this spring, the anomaly has been stuck near -1.5 million sq. km. for half of the year. This year’s minimum anomaly was eclipsed only by 2007’s in an absolute sense. The 2007 anomaly also spent more time at or below the anomaly measured this year, but this year has clearly been more negative for longer than during either 2008 or 2009. The change in September ice extent has been measured at -11.5% per decade by the NSIDC.
More important than areal extent, however, is the volume of ice. Why? If two years had the exact same minimum areal extent, say 3 million square kilometers, but the second year had thinner ice than the first year, the second would have less ice volume. If too much ice in the vertical dimension melts, the ice in the horizontal dimensions becomes easier to melt every summer. To give you a better idea of how Arctic ice volume has changed over the satellite record, click the following link, which shows that ice volume has been decreasing for decades, but has worsened considerably in the past 5 years. The graph shows how a particular day’s ice volume compares to the climatological record, which in this case extends from 1979-2009. A record low volume was recorded this summer. Keeping my simplified explanation above in mind, look at the difference between the 2007 minimum and the 2010 minimum. The 2010 minimum was 3 thousand cubic kilometers lower than the 2007 minimum, even though the 2007 areal extent was 600,000 square kilometers lower than 2010’s. That’s very bad news moving forward.
Arctic Pictures and Graphs
Here is a satellite representation of Arctic sea ice conditions from September 19th, when this year’s minimum occurred:
Compare that with the similar picture from April, close to when this year’s maximum occurred:
The image I don’t have is the one showing what the climatological average conditions look like. The closest I have was in last month’s State of the Poles post where I described the August extent as lower than the average. Suffice it to say that the edge of the minimum ice pack in 2010 was much smaller than the average.
The state of Antarctic sea ice at the end of September 2010 was little changed from conditions found throughout August. In fact, those conditions have extended into the first three weeks of October as well. There is nothing surprising or anomalous about those conditions. Antarctic sea ice extent has bounced around 19 million sq. km. for almost three months now. The early August sea ice extent was a little higher than average conditions, then it fell to near average during September. The early October Antarctic sea ice extent is somewhat similar to the Arctic’s March-April sea ice extent: on the high end of the scale. The yearly melt season is set to begin. We’ll be able to see the Antarctic’s minimum extent sometime in February 2011.
You can find the NSIDC’s October report here. The page is dynamic, so if you’re reading this after October 2010, that month’s report will show up first. If that’s the case, you can look for whatever report you’re looking for on the top pull-down tab on the right-hand side of the page.
Cross-posted at SquareState.