| Summary: | The meridional overturning circulation (MOC) is part of a global ocean circulation that redistributes heat from Equatorial to Polar regions. In the Atlantic, the MOC (AMOC) carries heat northward (the Atlantic Heat Conveyor) which is released to the atmosphere and maintains UK temperatures between 3 to 5°C higher than they would otherwise be. However, the present strength and structure of the MOC may not continue. The IPCC Fourth Assessment Report (IPCC, 2007) concludes that there is greater than 90% chance that the AMOC will slow by up to half by 2100, compared to pre-industrial levels, offsetting some of the warming over the European sector of the North Atlantic, and contributing to the rate of Atlantic sea-level-rise. The IPCC also concluded that there is less than 10% chance of abrupt changes during the 21st Century. Daily observations using the RAPID MOC mooring array at 26°N are providing a continuous and growing time series of the AMOC strength and structure, the time series is not yet sufficiently long to determine if there is a long-term trend in the AMOC. There was a significant reduction in the AMOC in 2009-2010 that has since recovered. The relationships between the AMOC reduction and the anomalous winter weather over the UK at the same time are not yet understood. Other observations do not at present provide a coherent Atlantic wide picture of MOC variability, and there is little evidence of any long-term slowing. Despite substantial progress over recent years in understanding and modelling the AMOC, projections of its future fate are still subject to significant uncertainty.
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