I think it's irresponsible of @UNFCC to not only report the Arctic Amplification-weak jet stream theory as an accepted fact (which it isn't: https://www.nature.com/articles/s41558-019-0662-y) but also to try and claim it can be immediately attributed to the cold-air outbreak over North America. https://twitter.com/UNFCCC/status/1361355803949756416
For example, we found that [in the Atlantic annual-mean] while the temperature gradient has been weakening in the lower troposphere (due to Arctic Amplification), the upper-level gradient has been strengthening, effectively offsetting each other https://www.nature.com/articles/s41586-019-1465-z
Increased shear in the North Atlantic upper-level jet stream over the past four decades

The North Atlantic jet stream has become 15 per cent more sheared in the upper atmosphere since 1979, an expected consequence of climate change, and consistent with increased aircraft turbulence.

https://www.nature.com/articles/s41586-019-1465-z
Further, Russell Blackport & @polar_james reported in 2020 that the link between waviness & temperature gradients "does not represent a forced response to Arctic amplification" https://advances.sciencemag.org/content/6/8/eaay2880
Insignificant effect of Arctic amplification on the amplitude of midlatitude atmospheric waves

Whether Arctic amplification has contributed to a wavier circulation and more frequent extreme weather in midlatitudes remains an open question. For two to three decades starting from the mid-1980s,...

https://advances.sciencemag.org/content/6/8/eaay2880
This is not to say Arctic Amplification cannot, has not, or will not impact jet stream behaviour. But in real-time, all we can and should say is this is an extreme example of internal variability (i.e., vortex disruption following a major SSW) & cold-air outbreaks are declining.
. @GeoffVallis, who literally wrote *the* book on atmospheric dynamics, says it well - https://twitter.com/GeoffVallis/status/1361444674653855748?s=20
Great thread from @Marlene_Climate: https://twitter.com/Marlene_Climate/status/1361618679973224452?s=20
You can follow @SimonLeeWx.
Tip: mention @twtextapp on a Twitter thread with the keyword “unroll” to get a link to it.

Latest Threads Unrolled:
Those who think consciousness raising & movement building are disconnected, or even a distraction from electoral politics have not paid attention to the history of social change.In this thread, we
Read more
The 2020s will be known as the Remote Work decadeA few predictions of what is likely to emerge[ a thread ] Third Space: Office and Working from Home will
Read more
1/29: Have you ever had a concept explained to you that helps frame complex issues you’ve been wrestling with and opens your eyes to new possibilities? A concept that I
Read more
By continuing to use the site, you are consenting to the use of cookies as explained in our Cookie Policy to improve your experience.