It seems that global warming causes everything. It is said to be simultaneously responsible for below average sea ice extent in the Arctic and record high sea ice extent in the Antarctic. Whether temperatures are warmer or colder, alarmists blame it on global warming. Such was the case last winter. When the circumpolar vortex dipped south to cause ‘usually” cold weather in North America, it was blamed on global warming. But was that cold spell really unusual?
Some researchers decided to find out by studying January temperatures for the period 1948-2013. The paper is:
Ballinger, T.J., Allen, M.J. and Rohli, R.V. 2014. Spatiotemporal analysis of the January Northern Hemisphere circumpolar vortex over the contiguous United States. Geophysical Research Letters 41: 3602-3608.
The paper was reviewed at CO2Science.com here.
The four U.S. researchers report that “the spatial features of the January 2014 USPV [United States Polar Vortex] were not extreme relative to certain 1948-2013 Januaries,” as they note that the USPV of January 2014 only ranked as having “the sixth most southerly latitude, tenth most westerly longitude, and seventh largest area.” Nor were the temperatures of the polar air the USPV brought with it ultra-extreme, as they say that the mean surface air temperatures of January 2014 were merely among “the coldest 10% of Januaries on record,” as recorded within the 120-year history of the National Climatic Data Center (NCDC, 2014) archive for several Midwestern and Southern states.
So, in spite of all the media hype, last winter’s cold spell was not unusual, not unprecedented, nor unnatural. And, it had nothing to do with global warming. It has to do with multi-decadal oscillations in atmospheric and oceanic circulation regimes, such as the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation that can amplify or diminish longer term atmospheric warming or cooling. See The Stadium Wave Hypothesis.
There is also the minor detail that there has been no net global warming since 1998.