Modelled changes to tropospheric circulation associated with changes in stratospheric water vapour

We have modelled the climatic effects of observed changes in stratospheric water vapour amounts in the last 50 years in two different climate models: an intermediate global circulation model (IGCM) and a state of the art atmosphere circulation model (the Hadley Centre Global Atmospheric model HadGAM1). In addition to already known global effects, we find circulation changes in the stratosphere and troposphere associated with the pattern of radiative cooling. The stratospheric water vapour increase leads to an increase in the North Atlantic Oscillation (NAO) Index in both models. We comment on the implications of these results for climate modelling.