Thread by @Knutti_ETH

1/ The link between changes in the Arctic and clear changes in the frequency or duration of (winter) weather patterns have been debated for years. I've always been rather skeptical.
nature.com/articles/nclim…

2/ Now the evidence is growing that some of the proposed changes are not straightforward.
nature.com/articles/s4155…

3/ Blackport @polar_james argue here that "the Arctic influence on mid-latitudes is small compared to other aspects of climate var., and that obs. periods of strong correlation are an artefact of internal variability".
nature.com/articles/s4155…

4/ This is consistent with our own analysis that models (showing little dyn change) and observations are in agreement when accounting for natural climate variability.
agupubs.onlinelibrary.wiley.com/doi/full/10.10…

5/ And the proposed "regime shifts" in the 80ies in Europe are likely a simple sum of long term warming plus random variability.
iopscience.iop.org/article/10.108…

6/ Experiments with one coupled model prescribing sea ice changes also didn't show colder or snowier winters.
agupubs.onlinelibrary.wiley.com/doi/full/10.10…

7/ A new analysis of all available global models shows no clear changes in the frequency or persistence of weather patterns for Central Europe that exceeds variability.
agupubs.onlinelibrary.wiley.com/doi/full/10.10…

8/ Of course that does *not* imply that nothing will change. Or that everything is clear. Models may not capture all feedbacks. There are plenty of open questions regarding changes in the dynamics. Others are better qualified to comment on that.

9/ Absence of evidence is not evidence of absence.

From a risk perspective, not knowing the change differs massively from knowing things won't change.

10/ Overall, I would argue there is growing evidence for changes in extremes that are directly caused by warming, in particular more hot days, heat waves, and heavy precipitation (moisture holding capacity of warmer air).

11/ Forced changes in the dynamics and their impact on mid-latitude winter weather are more complex and unlikely to dominate changes in the near future. And natural variations in atmospheric dynamics unrelated to climate change will remain large and have impacts.

12/ So we can't exclude or cold a snowy winter 2020/2021. But unfortunately climate change on the long run will very likely make winters warmer in the Alps, with less snow in low altitudes.

13/ (German link)
meteoschweiz.admin.ch/home/aktuell/m…

14/ Further references in this letter:
nature.com/articles/s4155…

15/ Another new comment questioning the dynamic link between the Arctic and winters in Europe.
nature.com/articles/s4155…