As the Arctic warms, atmospheric changes may paradoxically bring colder winters to North America and Eurasia. If a warm Arctic leads to an early breakup of the polar vortex then the mid-latitudes will be inundated with cold Arctic air during mid-winter but spring comes early since much of the cold air gets dissipated early.
Earth Observatory:stratosphere influences winter weather
Wunderground: winter La Nina forecast
NOAA Arctic "Report Card"
"There is evidence that the effect of higher air temperatures in the lower Arctic atmosphere in fall is contributing to changes in the atmospheric circulation in both the Arctic and northern mid-latitudes. Winter 2009-2010 showed a new connectivity between mid-latitude extreme cold and snowy weather events and changes in the wind patterns of the Arctic; the so-called Warm Arctic-Cold Continents pattern."
Paleorecord of arctic warming indicates these conditions are unprecedented in at least the last few thousand years. For more information on climate change-linked weather anomalies, check out the 2010 drought in the Amazon.