  Climate variability on centennial timescales has often been linked to
internal variability of the Atlantic Meridional Overturning Circulation (AMOC).
However, due to the scarceness of suitable paleoclimate proxies and long
climate model simulations, large uncertainties remain on the magnitude and
physical mechanisms driving centennial-scale AMOC variability. For these
reasons, we perform, for the first time, a systematic multi-model comparison of
centennial-scale AMOC variability in pre-industrial control simulations of
state-of-the-art global climate models. Six out of nine models in this study
exhibit a statistically significant mode of centennial-scale AMOC variability.
Our results show that freshwater exchanges between the Arctic Ocean and the
North Atlantic provide a plausible driving mechanism in a subset of models, and
that AMOC variability can be amplified by ocean-sea ice feedbacks in the
Labrador Sea. The amplifying mechanism is linked to sea ice cover biases, which
could provide an observational constraint for centennial-scale AMOC
variability.
