From November 2013 through January 2014, the jet stream took on a remarkably extreme and persistent shape over North America and Europe. This global river of eastward-fl owing winds high in the atmosphere dipped farther south than usual across the eastern U.S., allowing the notorious "polar vortex" of frigid air swirling over the Arctic to plunge southward, putting the eastern two thirds of the country into a deep freeze. Ice cover on the Great Lakes reached its second-greatest extent on record, and two crippling snow-and-ice storms shut down Atlanta for multiple days.

At the same time, a stubborn ridge of high pressure hunkered down over California, creating the warmest winter on record there. Although the balminess may sound nice, the resulting drought became the worst since record keeping began in the late 1800s, causing billions of dollars in agricultural losses.

The jet stream's contortions also pummeled Europe, where a succession of intense storms led to additional billions of dollars of damage. In England and Wales the winter was the wettest since at least 1766. Much of the rest of Europe basked in exceptional warmth: Norway suffered unprecedented January wildfires, and Winter Olympics officials in Sochi, Russia, struggled with melting ski slopes. In May nearly one third of the entire country of Bosnia was fl ooded by a massive, swirling rainstorm. ...