The term “polar vortex” has become a new buzzword, alongside “superstorm” or “bombogenesis,” terms used in the media to refer to unusual, news-worthy weather patterns. It’s easy to think the word means a swirling storm of unusually cold air, and some people are starting to use it to refer to any cold snap. But that isn’t what it means.
The polar vortex is actually a persistent weather pattern that forms around the north or south pole and acts to keep cold air concentrated near the pole during winter. What happened earlier this month was not that a polar vortex occurred or that the polar vortex was stronger than normal, but rather that the polar vortex was weaker than normal and it leaked.
During the January cold snap, the eastern and central parts of the United States were, of course, unusually cold. But, at the same time, northern Canada was warmer than usual, because the cold air that normally sits there had moved south. So January was not actually colder than normal, it’s just that the cold air was in an unusual place.
Actually, for areas not affected directly by the leaky vortex, temperatures that week were mostly normal or even unusually warm. Much of the American and Canadian West were warmer than normal for this time of year. Europe was very warm. Australia is having one of its warmest summers on record, with temperatures so hot in some places that week that wild animals, some of them endangered species, died in huge numbers.
Of course, mild weather in the west does not make an exciting news story. State disasters declared in New York and Illinois, schools closed as far south as Florida, and dozens of people injured or dying from the cold all make for a lot of media attention. Americans can be forgiven, at least initially, for thinking that the Polar Vortex froze the whole world.
But after that initial reaction (“I can’t feel my feet, therefor there is no warmth anywhere”), we really should get some perspective.
Not only were some parts of the planet very warm this January, but in terms of global temperatures, this past December was the third hottest December since 1880, when record-keeping began. That whole year, 2013, tied with 2003 as the fourth warmest year on record. Further, even many of the areas affected by the cold snap were only brutally cold in comparison to the much warmer temperatures of recent decades. Within living memory that kind of cold would have been considered chilly, but not dramatically so.
It is true that genuine cooler periods happen occasionally, when the world actually is slightly cooler for a while. But Peyton Manning sometimes throws interceptions and few people doubt he’ll get in the Hall of Fame one day. Part of scientific literacy means understanding that there is a difference between regional cold weather and global climatic trends, and a difference between variation along a trend line and the trend itself.
And, counter-intuitive as it may seem, it is quite possible that the frigid blast the Eastern U.S. received is actually one more symptom of global warming.
The polar vortex that normally keeps the coldest air confined to the poles is ringed by the jet stream, a current in the upper atmosphere that is in turn created by the contrast in temperature between polar and tropical air. That is, the difference in temperature exacerbates itself by creating a wind pattern that keeps the two air masses largely separate. Since the poles are warming faster than the rest of the planet is, climate change could involve a weakening of the jet stream. That would allow the polar vortex to leak more often, producing a warmer world overall, but more frequent cold snaps in unexpected places.
Global warming means a warmer globe, and that is what we are getting. But that doesn’t mean an end to winter everywhere, nor does it mean an even, easy to predict warmth. In practical, locally observable terms, “global weirding” may be a much more accurate name. For parts of the eastern U.S. to be colder than Alaska is definitely weird.