There has been quite a bit of commentary on the web with respect to the current absence of continued freeze up of Arctic Sea ice as monitored by the National Snow and Ice Data Center. Mark Serreze has graciously permitted Climate Science to post the explanation for this lack of increase. His comment follows:
“We’ve been getting a lot of questions about this. We are quite certain that the almost complete lack of increase in ice extent since about December 10 is real. Satellite-derived ice extent from the SSM/I (Special Sensor Microwaver/Imager) used to create the time series on our website was checked against extent based on the AMSR (Advanced Microwave Sounding Radiometer) instrument. AMSR shows the same pattern. This gives us independent confirmation. The past 10 days has seen a very unusual atmospheric pattern. It has been very warm over the Arctic Ocean, and wind patterns have favored a compact ice cover. While the lack of increase in ice extent is certainly quite unusual as well as interesting, we would not read too much into it right now, at it is just weather. It will be interesting to see what happens over the next week. [The] issue with Chapman’s site, apparently, is that they are looking at area (concentration weighted) versus extent (part of ocean covered with ice with at least 15% concentration) The compaction that seems to be going on could give a flat line in extent but still a rise in area. In other words, the issue may be that we are looking at two different measures of ice conditions. Also, it’t not clear (I’ll have to check) how current Chapman’s data are. We had a delay in posting for awhile because of some data dropouts. “