Editing IPCC:AR6/WGI/Chapter-9 (section)

=== Ocean Circulation ===

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'''The Atlantic Meridional Overturning Circulation (AMOC) will''' ''very likely'' '''decline over the 21st century for all SSP scenarios. There is''' ''medium confidence'' '''that the decline will not involve an abrupt collapse before 2100.''' For the 20th century, there is ''low confidence'' in reconstructed and modelled AMOC changes because of their ''low agreement'' in quantitative trends. The ''low confidence'' also arises from new observations that indicate missing key processes in both models and measurements used for formulating proxies and from new evaluations of modelled AMOC variability. This results in ''low confidence'' in quantitative projections of AMOC decline in the 21st century, despite the ''high confidence'' in the future decline as a qualitative feature based on process understanding. {9.2.3}

'''Southern Ocean circulation and associated temperature changes in Antarctic ice-shelf cavities are sensitive to changes in wind patterns and increased ice shelf melt''' ( ''high confidence'' ''').''' However, limitations in understanding feedback mechanisms involving the ocean, atmosphere and cryosphere, which are not fully represented in the current generation of climate models, generally limit our confidence in future projections of the Southern Ocean and of its forcing on Antarctic sea ice and ice shelves. {9.2.3, 9.3.2, 9.4.2}

'''Many ocean currents will change in the 21st century as a response to changes in wind stress associated with anthropogenic warming''' ( ''high confidence'' ''').''' Western boundary currents have shifted poleward since 1993 ( ''medium confidence'' ), consistent with a poleward shift of the subtropical gyres. Of the four eastern boundary upwelling systems, only the California Current system has experienced some large-scale upwelling-favourable wind intensification since the 1980s ( ''medium confidence'' ). In the 21st century, consistent with projected changes in the surface winds, the East Australian Current Extension and Agulhas Current Extension will intensify, while the Gulf Stream and Indonesian Throughflow will weaken ( ''medium confidence'' ). Eastern boundary upwelling systems will change, with a dipole spatial pattern within each system of reduction at low latitude and enhancement at high latitude ( ''high confidence'' ). {9.2.1, 9.2.3}

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