Despite wind chills nearing -60 degrees Fahrenheit in Chicago and temperatures that left some parts of Canada colder than Mars, Arctic sea ice is still melting, atmospheric CO2 concentrations are still climbing and climate change is predicted to pose a far greater threat to the planet than many scientists thought.
Winters have become increasingly warmer over the past century, and despite the recent bout of subzero temps, global warming can make extreme weather events like the polar vortex even worse. In layman's terms, as the planet warms and Arctic sea ice melts, the northern polar region equalizes a bit with temperatures farther south, causing the jet stream that forms a circular band around the northern latitudes to slow down.
This jet stream usually holds the far colder Arctic air in place with winds in excess of 100 mph, but pockets of cold can escape at times when the stream slows down, according to Time.
Also: frost quakes!