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.

For a full understanding of the global climate system, it is imperative to integrate research on empirical climate reconstruction with physical modelling studies of the Earth's climate, using numerical models of varying complexity to address important questions about the attribution of past and future climate changes to specific natural and anthropogenic factors. The focus of this project was on testing various hypotheses about the possible causes of the Little Ice Age. A carefully-designed set of model experiments (incorporating novel methods of assimilating information on climate time scales) were proposed, with the outputs assessed through comparison against empirical palaeoclimate evidence for climate variations over the past millennium. Specifically exploreed whether the Little Ice Age climate could have been generated by one or more of the following factors: a weakening of the Atlantic thermohaline circulation; the persistence of a generally negative North Atlantic Oscillation; or reduced radiative forcing (by increased volcanic activity, reduced solar insolation and lower greenhouse gas concentrations relative to the present).