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.

To make the best use of the historical research ship records as well as new observations from autonomous ocean profiling floats and special observing programs such as Rapid climate change, it was proposed to assimilate all of the available data from the past 40 years into a high quality ocean circulation model that can represent complete fields of ocean properties. In this way derived quantities such as the north-south mass and heat transports which are vital to understanding the oceans role in controlling climate, could be determined. The project also put into context the various timeseries of observations that have been compiled from local regions which suggest that important changes in ocean circulation and transports have been ongoing in the past decades. These timeseries have been put into a basin scale and global scale context of ongoing change. The program determined the relationship between hydrographic signals in different parts of the ocean basins (particularly the N Atlantic). The program provided a method for assimilating data from the thermohaline monitoring arrays into an ocean model that could then be used as part of a coupled climate model for multi-annual climate prediction.