The polar vortex, a jet stream swirling around the north pole, has weakened the past two winters, allowing plumes of cold air to slip south. But to most climatologists, two years don't make a trend. Atmospheric scientist John Wallace talks about why he is cautious about linking weird weather to global warming.
Two Cold Winters Don't Make A Climate Trend
Fri, 01/28/2011 - 10:41am