It is an unusual winter

While our impulse may be to say a) "Worst winter ever." or b) "This is an old-fashioned winter," there appears to be something unusual about this winter and last.
The Arctic polar vortex, a large and irregularly-shaped low pressure system, has shifted out of its typical location, pushing cold air first to Europe earlier in the season and now to us. The result is a blast of cold air. The other effect, however, is that parts of the Arctic are experiencing much warmer than normal temperatures. The late freeze of the ice cap is, as you might expect, impacting the lifestyles of animals and people who live in the high Arctic. You can read more in this New York Times article, Topsy-Turvy Weather - U.S. Is Frigid, and Arctic Warmer Than Usual .
We can't call this a result of global warming based on a couple of weird winters. We'll just say that the impact is noticeable.
For example, the North's most famous resident didn't even bother to go back home after his December extravaganza, finding the climate on Brattle Street much to his liking.