Physical and Unphysical Causes of Nonstationarity in the Relationship
between Barents-Kara Sea Ice and the North Atlantic Oscillation
Abstract
The role of internal variability in generating an apparent link between
autumn Barents-Kara sea ice (BKS) and the winter North Atlantic
Oscillation (NAO) has been intensely debated. In particular, the
robustness and causality of the link has been questioned by showing that
BKS-NAO correlations exhibit nonstationarity in both reanalysis and
climate model simulations. We show that the lack of ice observations
makes analysis of nonstationarity using reanalysis questionable in the
period 1950-1970 and effectively impossible prior to 1950. Model
simulations are used to corroborate an argument that nonstationarity is
nevertheless expected due to changes in the ice edge variability due to
global warming. Consequently, changes in BKS-NAO correlations over time
may simply reflect that the ice edge has moved, rather than that there
is no causal link. We discuss potential implications for analysis based
on coupled climate models, which exhibit large ice edge biases.