Rapid Climate Change (RAPID) was a £20 million, six-year (2001-2007) programme for the Natural Environment Research Council. The programme aimed to improve the ability to quantify the probability and magnitude of future rapid change in climate, with a main (but not exclusive) focus on the role of the Atlantic Ocean's Thermohaline Circulation.

The main tools that are used for making projections of climate change in the coming century resulting from greenhouse-gas and other emissions are detailed coupled three-dimensional models of the atmosphere and ocean. However, such models give widely different results for some important aspects of climate change, thus limiting our ability to make practically useful projections. One such aspect is changes that may happen in the Atlantic Ocean thermohaline circulation, often referred to as the Gulf Stream. This circulation transports a great deal of heat northwards. If it weakened, future warming in Europe in particular could be reduced or possibly reversed. The spread of model results basically reflects limitations in current understanding of how the large-scale climate system operates. The aim of this project was to identify which are the most important aspects of that uncertainty by making comparisons of the responses simulated by a range of climate models. The results were intended to help improve the models by focusing attention on the aspects which require further theoretical or observational study.