Holland, M.M., and C.M. Bitz, 2003:
Polar amplification of climate change in coupled models
Submitted to Climate Dynamics


The northern hemisphere polar amplification of climate change is documented in models
taking part in the Coupled Model Intercomparison Project and in the new version of the
Community Climate System Model. In particular, the magnitude, spatial distribution, and
seasonality of the surface warming in the Arctic is examined and compared among the
models. The range of simulated polar warming in the Arctic is from 1.5 to 4.5 times the
global mean warming. While ice-albedo feedback is likely to account for much of the
polar amplification, the strength of the feedback depends on numerous physical processes
and parameterizations which differ considerably among the models. Nonetheless, the
mean sea ice state in the control (or present) climate is found to influence both the
magnitude and spatial distribution of the high latitude warming in the models. In
particular, the latitude of the maximum warming is correlated inversely and significantly
with sea ice extent in the control climate. Additionally, models with relatively thin Arctic
ice cover in the control climate tend to have higher polar amplification. An
intercomparison of model results also shows that increases in poleward ocean heat
transport at high latitudes and increases in polar cloud cover are significantly correlated
to amplified Arctic warming. This suggests that these changes in the climate state may
modify polar amplification. No significant correlation is found between polar amplification and the control climate continental ice and snow cover.

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