We have seen a quantum jump in extreme weather events in the Northern Hemisphere in the last several years. Droughts, deluges, and heat waves are increasingly getting “stuck” or “blocked,” which in turn worsens and prolongs their impact beyond what might be expected just from the recent human-caused increase in global temperatures.
A growing body of research ties that unexpected jump to a weakening of the jet stream — in particular to “more frequent high-amplitude (wavy) jet-stream configurations that favor persistent weather patterns,” as a new study puts it.
Much of this new research ties the weakening jet stream to “Arctic amplification (AA) — defined here as the enhanced sensitivity of Arctic temperature change relative to mid-latitude regions,” in the words of the new study, “Evidence for a wavier jet stream in response to rapid Arctic warming” by Jennifer Francis and Stephen Vavrus. But that is no by no means a universally accepted explanation. I’ll review some of the evidence in this post.