Preprints
https://doi.org/10.5194/wcd-2022-32
https://doi.org/10.5194/wcd-2022-32
 
20 Jun 2022
20 Jun 2022
Status: this preprint is currently under review for the journal WCD.

Reconciling conflicting evidence for the cause of the observed early 21st century Eurasian cooling

Stephen Outten1,2,, Camille Li3,2,, Martin P. King3,4,2, Lingling Suo1,2, Peter Y. F. Siew3,2, Richard Davy1,2, Etienne Dunn-Sigouin3,2, Shenping He3,2, Hoffmann Cheung5,6,2, Erica Madonna3,2, Tore Furevik1,2, Stefan Sobolowski4,2, Thomas Spengler3,2, and Tim Woollings7 Stephen Outten et al.
  • 1Nansen Environmental and Remote Sensing Center, Bergen, Norway
  • 2Bjerknes Centre for Climate Research, Bergen, Norway
  • 3Geophysical Institute, University of Bergen, Bergen, Norway
  • 4NORCE Norwegian Research Centre, Bergen, Norway
  • 5School of Atmospheric Sciences & Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Zhuhai, China
  • 6Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai, China
  • 7Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, United Kingdom
  • These authors contributed equally to this work.

Abstract. It is now well established that the Arctic is warming at a faster rate than the global average. This warming, which has been accompanied by a dramatic decline in sea ice, has been linked to cooling over the Eurasian subcontinent over recent decades, most dramatically during the period 1998–2012. This is a counterintuitive impact under global warming given that land regions should warm more than ocean (and the global average). Some studies have proposed a causal teleconnection from Arctic sea ice retreat to Eurasian wintertime cooling; other studies argue that Eurasian cooling is mainly driven by internal variability and the relationship to sea ice is coincidental. Overall, there is an impression of strong disagreement between those holding the “ice-driven” versus “internal variability” viewpoints. Here, we offer an alternative framing showing that the sea ice and internal variability views can be compatible. Key to this is viewing Eurasian cooling through the lens of dynamics (linked primarily to internal variability with a small contribution from sea ice; cools Eurasia) and thermodynamics (linked to sea ice retreat; warms Eurasia). This approach, combined with recognition that there is uncertainty in the hypothesized mechanisms themselves, allow both viewpoints (and others) to co-exist and contribute to our understanding of Eurasian cooling. A simple autoregressive model shows that Eurasian cooling of this magnitude is consistent with internal variability, with some periods being more susceptible to strong cooling than others. Rather than posit a “yes-or-no” causal relationship between sea ice and Eurasian cooling, a more constructive way forward is to consider whether the cooling trend was more likely given the observed sea ice loss, as well as other sources of low-frequency variability. Taken in this way both sea ice and internal variability are factors that affect the likelihood of strong regional cooling in the presence of ongoing global warming.

Stephen Outten et al.

Status: open (until 01 Aug 2022)

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Stephen Outten et al.

Stephen Outten et al.

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Short summary
While the Arctic is warming rapidly, some counterintuitive regional impacts have emerged, including the pronounced cooling over the Eurasian subcontinent that has been linked to retreating Arctic sea ice. However, there is strong disagreement among the scientific community around the strength and even existence of this link, as well as the possible causes of Eurasian cooling. Here we provide a review of the state of understanding and a perspective that helps reconcile apparent disagreements.