Two competing effects influence our northern winters:

#1 Global warming.

#2 Increasing polar air outbreaks due to stratospheric polar vortex disturbances.

In the long run #1 wins - our winters are getting warmer. 1/🧵 Image
That's expected as #2 just happens occasionally, and polar air is also getting warmer.

Some people point to long-term warming trends to cast doubt on whether #2 is even real, but that is a non-sequitur. It just means #1 wins in the long run. 2/🧵 Image
That disturbed stratospheric polar vortex states are linked to polar air outbreaks and thus cold extremes either in Eurasia or the US is shown by data analysis:… 3/🧵
Objective cluster analysis of polar vortex states shows that cluster 4 is linked to cold in the US, cluster 5 to cold in Eurasia. 4/🧵 Image
Do these clusters increase in prevalence? The reanalysis data shows they do over the period 1979-2018. And this can explain why Eurasian winters haven't warmed more:… But of course that could be just due to random variability. 5/🧵 Image
On the other hand there are plausible mechanisms that link this increasing polar vortex instability to Arctic warming and sea ice loss. Causal effect network analysis (a data correlation method able to tease out causal links) suggests that:… 6/🧵 Image
Furthermore, analysis of 35 CMIP5 models shows that the sea ice loss effect, though weaker in the models than in the observational data, "can explain all of the projected ensemble-mean stratospheric polar vortex weakening":… 7/🧵 Image
To finish off, a fun fact: in 2014 right-wing US commentator Rush Limbaugh claimed the polar vortex was invented by the left... Against that speaks that it's already in the 1959 AMS Glossary of Meteorology. 8/🧵 Image
And a bunch of relevant references. Image

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More from @rahmstorf

Nov 23
"Wenn die auf sozialen Medien bei mir kommentieren blocke ich die einfach. Es ist alles hundert mal widerlegt worden, und wir haben einfach nicht Zeit uns damit jetzt noch aufzuhalten."
Dabei geht’s natürlich nicht um andere Meinungen - die sind immer ein normaler und wichtiger Teil des wissenschaftlichen Diskurses.
Es geht um falsche und unbelegte Behauptungen, gefälschte Grafiken, Verschwörungstheorien und Beleidigungen.
Read 4 tweets
Nov 13
For all interested in the tipping point of the Atlantic overturning circulation : here's Henk Dijkstra's recent talk.
The tipping point has been confirmed in a state-of-art climate model, and a novel early warning indicator suggests we're heading there.

The novel early warning indicator is based on a diagnostic I proposed in this paper in 1996:…
And the hysteresis in the coupled GCM is consistent with our hysteresis intercomparison results for intermediate complexity models, published in 2005. That is important confirmation that this holds for the full model complexity spectrum!
Read 4 tweets
Oct 30
There's more happening to weather extremes now than can be explained by thermodynamics, i.e. everything getting warmer, evaporation increasing, the atmosphere holding more energy and water.
Also changing: jet stream, polar vortex, planetary waves & Atlantic ocean circulation.

Some commentators (surprise!) didn’t get the key point: that climatologists distinguish between ‘thermodynamic’ and ‘dynamic’ effects of climate change. So far we’ve mostly seen thermodynamic effects on extremes, but we argue there’s more: we can now also see changes in dynamics.
Examples thermodynamics:
-> heat extremes increase because CO2 traps more heat.
-> Extreme 🌧️ increases because warm air holds more moisture.

Example dynamics:
-> heat extremes increase much more in Europe than elsewhere, due to jet stream changes.
Read 4 tweets
Aug 17
Kann’s nur wiederholen:
Extremregen nimmt durch die Klimaerwärmung zu.
Physik ist verstanden.
Weltweite Datenauswertung bestätigt es.
Read 5 tweets
Aug 5
Extremregen nimmt durch die #Erderwärmung durch fossile Energie zu.
- Die Physik ist klar (warme Luft hält mehr Wasserdampf).
- Seit 30 Jahren von Klimamodellen vorhergesagt.
- Die Messdaten zeigen die Zunahme seit den 1990ern:
Die verlinkte Studie zeigt die globalen Daten. Für die Wetterstationen in Deutschland, Schweiz, Österreich und Niederlande belegt diese Studie der ETH Zürich von 2020 die signifikante Zunahme von Extremregen:…
Auch immer noch aktuell, nur ist die Zunahme in den Daten seither noch eindeutiger geworden:
Read 6 tweets
Jul 30
Zwei Millionen Menschen hier haben bisher meinen viralen Thread zum Kipppunkt der Atlantikzirkulation gesehen. Wer kein Englisch lesen mag, für den gibt's auf deutsch 4 aktuelle Infos zum Thema.
1. Meinen Blogartikel:
2. Meinen Spiegel-Kommentar:
3. Den ZEIT Video-Podcast mit Dilan Gropengiesser:
Read 5 tweets

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