A sensitivity experiment has been performed with a stratosphere-resolving GCM where the mean state and variability of the stratosphere have been altered. It is shown that this has a significant effect on the mean and variability of wintertime northern hemisphere surface climate. In particular it is shown that the stratosphere strongly contributes to the persistence of the surface Arctic Oscillation at lags of 10--25 days. This confirms the importance of the stratosphere on surface climate that has been inferred by recent studies examining the Arctic Oscillation in reanalysis datasets.