  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.

Atmospheric and Oceanic Physics