Greenhouse‐effect theory has predicted—first written by Svante Arrhenius in 1895—that lower atmospheric warming from increasing carbon dioxide would preferentially warm high latitude (polar) regions of the Northern Hemisphere. A hundred years later, computer models still predict the same, and it is a fact that this region has warmed much more than the rest of the globe.
Back‐of‐the‐envelope reasoning (usually not a good idea when addressing the incendiary minefield of global warming) suggests that this should produce weaker midlatitude storms. These are the garden‐variety low‐pressure systems (cyclones) that form as a result of bursts of kinetic energy (motion) supplied by the jet stream. The jet is a fast‐moving current in the mid‐and‐upper troposphere that is nature’s way of dissipating the potential energy difference between the (hot) tropics and the (cold) poles. Warm the poles preferentially and this temperature contrast declines, and so does the energy for cyclones. Less energetic cyclones generally means less severe weather, like floods, tornadoes and other pestilences.
Well, maybe not.
There is a new paper about to be published in Geophysical Research Letters that claims a positive relationship between the “Arctic amplification” of global warming and extreme weather outbreaks in the Northern Hemisphere mid‐latitudes. This is a significant finding if it proves to be true. However, the authors, Jennifer Francis and Steven Vavrus—despite being very enthusiastic—fail to convincingly make their case in light of other previous publications in the climate literature.
In their paper “Evidence Linking Arctic Amplification to Extreme Weather in Mid‐Latitudes” Francis and Vavrus argue that the differential rates of warming between the Artic and the mid‐latitudes of the Northern Hemisphere cause a slowdown in the eastward progression of weather systems driven by the jet stream, “which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.”
(This statement is reminiscent of the infamous phrase in the United Nations’ Intergovernmental Panel on Climate Change Second Assessment Report in 1995 that moved global warming from science to what the philosopher Karl Popper called “pseudo‐science.” The difference is that science (example: classical physics) can be “falsified” by critical observations, and pseudo‐science purports to explain everything. As the IPCC said, “Warmer temperatures will lead to a more vigorous hydrological cycle; this translates into prospects for more severe droughts and/or floods in some places and less severe droughts and/or floods in other places.” So much for falsifiability.)
The jet stream circumnavigates the North Pole, and “waves” move along it, such that its shape in not perfectly circular, but rather more meandering and ever changing. Like waves on a stretched string, short‐wavelength ones (of about 400 miles from peak‐to‐peak) move through the jet stream faster than long waves (which can cover thousands of miles). In fact, long waves can get ”stuck,” for various and sundry reasons, with little net movement. This is a situation known as “blocking,” and results in the same type of weather occurring over a particular region for a prolonged period of time. If that’s good weather, don’t look for scientists to blame greenhouse gases (where’s the incentive for that?); but if it’s bad weather, well, global warming!
Francis and Vavrus prefer the latter approach. From their conclusions: