There is no longer any doubt that human activities are causing changes in the Earth's climate. However, the patterns of future change are very uncertain. General circulation models (GCMs) of the atmosphere/ocean system are our best means of modelling future climate and assessing the extent and severity of changes. In this talk I will trace the development of GCMs over recent decades, and describe the make-up of a modern Earth System Model. I will review some results of recent climate simulations, with particular emphasis on the future wind climate of Ireland.