title: Abrupt cooling over the North Atlantic in modern climate models.
abstract: Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models' varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy.
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Institut Pierre Simon Laplace (IPSL), 91191 Gif-sur-Yvette, France.|Environnements et Paleoenvironnements Oceaniques et Continenteaux (EPOC), UMR CNRS 5805, Université de Bordeaux, 33615 Pessac, France.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Sgubin
authors.affiliation: Environnements et Paleoenvironnements Oceaniques et Continenteaux (EPOC), UMR CNRS 5805, Université de Bordeaux, 33615 Pessac, France.
authors.forename: Didier
authors.initials: D
authors.lastname: Swingedouw
authors.affiliation: Royal Netherlands Meteorological Institute (KNMI), 3730AE De Bilt, The Netherlands.|National Oceanography Centre (NOC), University of Southampton, Southampton SO14 3ZH, UK.
authors.forename: Sybren
authors.initials: S
authors.lastname: Drijfhout
authors.affiliation: Environnements et Paleoenvironnements Oceaniques et Continenteaux (EPOC), UMR CNRS 5805, Université de Bordeaux, 33615 Pessac, France.
authors.forename: Yannick
authors.initials: Y
authors.lastname: Mary
authors.affiliation: Institut de Mecanique et d'Ingenierie (I2M), Université de Bordeaux, 33615 Pessac, France.
authors.forename: Amine
authors.initials: A
authors.lastname: Bennabi