Global Warming Linked To More Extreme Weather And Weaker Jet Stream

http://thinkprogress.org/climate/2015/01/15/3612054/global-warming-extreme-weather/

by Joe Romm Posted on January 15, 2015

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.

Reinsurer Munich Re has the most comprehensive database of global natural catastrophes Their 2010 analysis, “Large number of weather extremes as strong indication of climate change,” concluded “it would seem that the only plausible explanation for the rise in weather-related catastrophes is climate change. The view that weather extremes are more frequent and intense due to global warming coincides with the current state of scientific knowledge.” For instance, a 2010 Journal of Climate study that found “global warming is the main cause of a significant intensification in the North Atlantic Subtropical High (NASH) that in recent decades has more than doubled the frequency of abnormally wet or dry summer weather in the southeastern United States.”

In 2011, Dr. Peter Höppe, Head of the Geo Risks Research Department at Munich Re explained what had persuaded him of the causal link:


For me the most convincing piece of evidence that global warming has been contributing already to more and more intense weather related natural catastrophes is the fact that while we find a steep increase in the number of loss relevant weather events (about tripling in the last 30 years) we only find a slight increase in geophysical (earthquake, volcano, tsunami) events, which should not be affected by global warming. If the whole trend we find in weather related disaster should be caused by reporting bias, or socio-demographic or economic developments we would expect to find it similarly for the geophysical events.

And that was before two years of off-the-charts extreme weather catastrophes, particularly in North America (in 2011, the head of NOAA said the record dozen billion-dollar weather disasters was “a harbinger of things to come.”

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