Some are saying that the extremely cold and snowy weather of January 2014 will be long remembered and the media seem to want to ensure that. Yes, some record lows have occurred but has it been that cold?
Dr. Stu Ostro’s meteorology blog at wunderground.com explains that the “Polar Vortex” that we’ve heard so much about is nothing new and is in fact, not unexpected. The polar vortex is a term given to the large circulation pattern in the upper atmosphere associated with winds circling the earth. The Alberta Clipper is another name for these circulation patterns when they develop over the North Pole. Temperatures plunged this year and snowfall spiked because the Arctic system dipped further south than usual and encountered another weather system moving eastward from the Pacific Ocean. There have been other recent vortices of similar intensity or even colder in 1996,1994, 1985, 1983, 1977 and earlier. In all likelihood this weather pattern has chilled Canada and the U.S. for centuries.
The polar vortex is not an effect of global warming which as the graph below shows, continues apace independently of this and other annual, regional phenomena. The graph from NASA shows that the secular temperature trend for the earth is clearly warming over the past century despite the short-term, smaller-scale dips in the 5- year running mean.
“Global warming”, of course, refers to temperatures that are averaged over the area of the entire earth (including the oceans), not just to regional or local areas despite our numbed fingers suggesting otherwise. All of North America, for example, occupies less than 5% of the world’s total area meaning that no matter how cold it was in the states and Canada, the global trend could be quite different. The map below of surface air temperatures produced by NOAA compares December 1, 2013 to January 7, 2014 to the same monthly interval for the 1981-2010 period in the Northern Hemisphere.
Clearly the area where temperatures have been above average well exceeds the area of below-average temperatures. Not shown is the Southern Hemisphere where despite some areas cooler than average, overall temperatures have been warmer than average, in some areas like Australia, very much so.