The science of deciphering how much long-term climate change influences shorter-term weather and climate events continues to blossom. On Thursday, the American Meteorological Society (AMS) released its fourth annual special issue of the Bulletin of the AMS devoted to these attribution studies. Launched in 2012 as an experiment, the project hit a nerve: researchers and the public were both intensely interested in the connection between human-produced greenhouse gases and high-profile, high-impact weather… The authors present their findings as an alternative to the “Francis hypothesis”–the concept put forth by Jennifer Francis (Rutgers University) and colleagues that a weaker, more meandering jet stream attributed to polar warming and reduced Arctic sea ice is leading to greater extremes and more “stuck” weather patterns. If anything, these authors suggest, high-latitude effects might be tamping down extremes rather than goosing them. “The decrease in variance is a plausible consequence of polar amplification of global warming, since a decrease in the pole-to-equator temperature gradient reduces the strength of fluid dynamical instabilities,” they write.