Some research suggests global warming is altering the jet stream, pushing Arctic air down to southern climes more frequently. But the jury is still out.
Climate scientists don't agree on what, if any, role global warming might be playing in a harsh end to winter. Arctic outbreaks of this year's severity occur naturally but are fairly uncommon.
A winter storm has sent frigid weather deep into the United States, setting low temperature records and leaving millions shivering in the dark because of power failures. Here's why the weather went wild, even as the globe is warming.
