The anti-scientific M.O. of some political conservatives was in full swing during the 'polar vortex,' as frigid weather brought south from the Arctic led many commentators to scoff, "look how cold it is, can you believe anyone thinks the Earth is getting warmer?" Coby Beck adds some perspective from climate historian Christopher C. Burt on A Few Things Ill-Considered, writing "cold snaps like this past week’s used to occur every couple of years in the 1800′s," and more like every 5-10 years in the 1900's. Meanwhile the last time it got so cold in the U.S. was twenty years ago. Coby says "what is remarkable is that this level of cold has become remarkable"—because it used to be commonplace. As the planet gets warmer, regional weather, unlike average global temperature, remains highly variable. Coby concludes, "this is just what scientists refer to as 'winter.'" Or what they used to, anyway.
Greg Laden offers a complementary interpretation, saying the polar vortex is the result of a jet stream increasingly unsettled by the warming of the Arctic. Per the theory of "weather whiplash," extreme temperatures might become more common as the energized jet stream contorts Arctic air. While the eastern U.S. was suffering bitter cold, northern Europe enjoyed unseasonal warmth; there's only so much Arctic air to go around. Which means the northern hemisphere can look forward to hot winter days as surely as very cold ones. The polar vortex was entirely consistent with global warming, and those who claimed otherwise wore their disingenuity on their sleeves.