We examine the sensitivity of the modelled climate of the third generation Hadley Centre climate model to changes in the parametrization of surface and boundary-layer fluxes under stable stratification. Replacing the model's standard parametrization with one in which fluxes decrease more rapidly with increasing stability generates statistically-significant changes in modelled 500 hPa height. The largest changes are seen across the North Atlantic and North Pacific and occur during Northern Hemisphere summer, when persistent stable atmospheric boundary layers form over the western sides of these oceans. The atmospheric response in a coupled version of the model is stronger than in the atmosphere-only version, suggesting that feedbacks involving sea surface temperatures, surface fluxes and atmospheric circulation are important in determining the response.