Eurasian cooling in response to Arctic sea-ice loss is not proved by maximum covariance analysis

TL;DR

This paper critically examines the claim that Arctic sea-ice loss causes Eurasian cooling, demonstrating that previous analyses using maximum covariance analysis are inconclusive and that atmospheric forcing likely drives sea-ice variability.

Contribution

The study challenges prior findings by showing that maximum covariance analysis does not prove causality from sea-ice loss to Eurasian cooling, emphasizing the importance of proper interpretation.

Findings

Maximum covariance analysis can be misinterpreted in climate studies.

Atmospheric forcing is more likely to drive sea-ice variability than vice versa.

Previous claims of Arctic sea-ice impact on Eurasian climate are not conclusively supported.

Abstract

The extent to which the ongoing decline in Arctic sea ice affects mid-latitude climate has received great attention and polarised opinions. The basic issue is whether the inter-annual variability in Arctic sea ice is the cause of, or the response to, variability in mid-latitude atmospheric circulation. A recent paper by Mori et al. (M19) claims to have reconciled previous conflicting studies by showing that a consistent mid-latitude climate response to inter-annual sea-ice anomalies can be identified in both the ERA-Interim reanalysis, taken as observations, and in an ensemble of atmosphere-only (AMIP) climate model simulations. We here demonstrate that such a conclusion cannot be drawn, due to issues with the interpretation of the maximum covariance analysis performed. After applying the M19 approach to the output from a simple statistical model, we conclude that a predominant atmospheric forcing of the sea-ice variability, rather than the converse, is the most plausible explanation of the results presented in M19.