Thread by @Marlene_Climate, Lots of discussions about the recent cold spell, the polar vortex and [...]

Lots of discussions about the recent cold spell, the polar vortex and the role of climate change... Here is my two cents on this:

1) I think it is very likely that the stratospheric polar vortex (SPV) played a major role in the recent cold air outbreak. The relationship between a weak SPV and cold weather is well documented, see also recent paper of @Domeisen_D @DrAHButler https://www.nature.com/articles/s43247-020-00060-z

Stratospheric drivers of extreme events at the Earth’s surface

Coupling between the stratosphere and the troposphere contributes to extreme events at the Earth’s surface, and can help with predictability on timescales from weeks to decades, according to a...

https://www.nature.com/articles/s43247-020-00060-z

2) SPV variability also contributed to the mid-latitude cold extremes (and related winter cooling tendency/weakened warming trend) over the last decades.
see e.g.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL072035 https://journals.ametsoc.org/view/journals/bams/99/1/bams-d-16-0259.1.xml

More-Persistent Weak Stratospheric Polar Vortex States Linked to Cold Extremes

Abstract The extratropical stratosphere in boreal winter is characterized by a strong circumpolar westerly jet, confining the coldest temperatures at high latitudes. The jet, referred to as the...

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL072035

3) The tricky question is, if and how much climate change played a role in this. There is evidence of Barents and Kara sea ice loss leading to a weakening of the SPV (e.g. https://journals.ametsoc.org/view/journals/clim/29/11/jcli-d-15-0654.1.xml) ...

Using Causal Effect Networks to Analyze Different Arctic Drivers of Midlatitude Winter Circulation

Abstract In recent years, the Northern Hemisphere midlatitudes have suffered from severe winters like the extreme 2012/13 winter in the eastern United States. These cold spells were linked to a...

https://journals.ametsoc.org/view/journals/clim/29/11/jcli-d-15-0654.1.xml

... but this comes with lots of uncertainties (see e.g. https://www.nature.com/articles/s41561-018-0059-y)

At this point we cant confirm the hypothesis but cannot rule it out either.

Consistency and discrepancy in the atmospheric response to Arctic sea-ice loss across climate models

Changes in Northern Hemisphere atmospheric temperature, pressure patterns and winds emerge as a consistent response to Arctic sea-ice loss in six coupled climate models.

https://www.nature.com/articles/s41561-018-0059-y

4) This implies the important question: What if Barents Kara sea ice loss plays a role? What would this mean for the SPV (and our weather) in the future? We address this here: https://wcd.copernicus.org/articles/1/715/2020/

The role of Barents–Kara sea ice loss in projected polar vortex changes

Abstract. The Northern Hemisphere stratospheric polar vortex (SPV) plays a key role in mid-latitude weather and climate. However, in what way the SPV will respond to global warming is not clear, with...

https://wcd.copernicus.org/articles/1/715/2020/

Key Result: Even a weak causal effect of BK sea ice loss has large implications for the SPV and sea ice loss in this region can explain all of the projected ensemble-mean weakening in CMIP5

bottom line: we need a better understanding of the different mechanisms (and associated risks) of how further Arctic changes (which are unfortunately certain in a warming climate) might affect our weather and climate. Follow e.g. @arctic_connect for updates on this topic

Latest Threads Unrolled: