Warm Arctic, Cold Northern Hemisphere
13.01.2010 - Atmosphere & Space, Ice & Snow, Arctic
Temperatures in the Arctic have skyrocketed to unusually high levels while much of the Northern Hemisphere has been experiencing frigid temperatures in the past few weeks. While one may be prone to blame global warming, scientists say this unusual pattern is part of natural variability, caused by a large area of high pressure over the Arctic and a large area of low pressure at the mid-latitudes.
While these areas of differing air pressure should normally mix in a natural Arctic oscillation, they have remained stationary in what is known as a negative phase of the oscillation (a positive phase would see low pressure over the Arctic and high pressure over the mid latitudes). December 2009 saw the most extreme negative phase seen since modern record-keeping began in 1950.
The negative phase appears to be in the process of weakening as both pressure areas have started to shift.
Average Arctic temperatures have been 5.6°C to 8.4°C above normal, and the extent of Arctic sea ice at the end of December remained some 920,000 km² below the December average for the period 1979 - 2000, although it was greater than the extent recorded in December 2006.
Although melting Arctic sea ice would mean an increase in sunlight absorption in the region, the current phase of the Arctic oscillation could have a counterbalancing effect by preventing the ice that covers the Arctic from being moved south to melt. Having the pressure zones where they are now could help multiyear sea-ice form, which has a higher albedo (an increased reflective capacity).
