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

The extent to which the ongoing decline in Arctic sea ice affects mid-latitude climate has received great attention and polarized opinions. The basic issue is whether the interannual variability in Arctic sea ice is the cause of, or the response to, variability in midlat- itude atmospheric circulation1. Mori et al.2 claim to have reconciled previous conflicting studies by showing that a consistent midlati- tude climate response to interannual sea-ice anomalies can be iden- tified between the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA-Interim), taken as observations, and an ensemble of atmosphere-only climate model simulations. Here we demonstrate that such a conclusion cannot be drawn, due to issues with the interpretation of the maximum covariance analysis performed. After applying the approach of Mori et al.2 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 a more plausible explanation of the results pre- sented in Mori et al.2.