Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the northern polar jet stream, the high, fast-moving torrent of air that circles the pole. The jet stream is slowing and meandering more, she proposes, causing extreme weather patterns to linger longer over North America. The idea has drawn extensive attention from the media, the public, and influential policymakers, such as White House science adviser John Holdren. Many researchers, however, are skeptical, and some have been vociferously critical. But Francis, whose life and work has been shaped by two round-the-world sailing adventures, has remained calm throughout the storm.