Noted: The idea, first put forth in a 2012 paper by Jennifer Francis, now at the Woodwell Climate Research Center, and Stephen Vavrus, at the University of Wisconsin at Madison, is that two well-established trends — Arctic amplification (intensified global warming at higher latitudes) and depleted sea ice — can force the polar jet stream to dip farther south, thus causing more intense bouts of winter weather than might have otherwise occurred.