photo: US Geological Survey/Creative Commons
New data coming out of the National Snow and Ice Data Center reveals two things which may at first seem contradictory at first but aren't: The extent of Arctic sea ice in February tied for a record low, while at the same time snow cover for January and February in the Northern Hemisphere remained extensive, ranking in the top six extents on record. Warmer Arctic Air Impacts Weather Patterns
Resolving the apparent but erroneous contradiction first, in the NSIDC's words:
Both linked to a strong negative phase of the Arctic Oscillation. A strongly negative AO favors outbreaks of cold Arctic air over northern Europe and the U.S., as many people experienced first-hand these last two winters. Whether this is a trend, or in any way linked to ongoing climate warming in the Arctic, remains to be seen.
NSIDC director Mark Serreze says, "Some scientists are beginning to suspect that the lack of sea ice allows the oceans to pump heat into the atmosphere in the Arctic in a way that could impact weather patterns such as the North Atlantic Oscillation. The idea is still very much in its infancy, but it's worth looking into."
NOAA on the impact of the NAO:
The [NAO] is a natural climate pattern that is the dominant mode of winter climate variability for the region, which ranges from central North America to Europe and into Northern Asia. A strongly negative NAO can indicate a breakdown of the Polar Vortex. Last winter, there were two extreme cold continent events...the breakdown of the Vortex, as measured by the NAO, was the most extreme on record for the past 145 years.
Clear Downward Trend in Winter Sea Ice
For February 2011, the average sea ice extent was 14.36 million square kilometers. This ties for the previous record low set in 2005. Sea ice was below normal in both the Atlantic and Pacific. Since it is winter sea ice did grow over the month, and at average rates, but NSIDC characterized the extent as "anomalously low" (it is a record low after all...). Overall the data shows that there is a clear downward winter trend.
Temperatures in the Arctic were 2-4°C higher than normal on average, with some areas showing particularly warmth. Over the East Greenland Sea and towards the North Pole, temps were 5-7°C higher than normal. At the other end of the scale, western and east-central Eurasia, as well as some parts of the Canadian Arctic, were 2-6°C below normal.
Extent of snow cover in January and February. In the bottom images blue is greater than normal snow cover; orange is lower than normal. Images: NSIDC
As for snow cover in the Northern Hemisphere, NSIDC data shows that 47 million square kilometers of land in January and 49 million square kilometers in February were covered in snow. For January that is the sixth-largest extent of snow cover since records began in 1966. Overall, snow cover in January was "unusually widespread" in the western and eastern United States, eastern Europe and in western China. February saw higher than normal snowfall in those regions, plus Tibet.