Causes of the rapid warming of the North Atlantic ocean in the mid-1990s

Robson, J. ORCID: https://orcid.org/0000-0002-3467-018X, Sutton, R. ORCID: https://orcid.org/0000-0001-8345-8583, Lohmann, K., Smith, D. and Palmer, M. D. (2012) Causes of the rapid warming of the North Atlantic ocean in the mid-1990s. Journal of Climate, 25 (12). pp. 4116-4134. ISSN 0894-8755 doi: 10.1175/JCLI-D-11-00443.1

Abstract/Summary

In the mid-1990s the subpolar gyre of the North Atlantic underwent a remarkable rapid warming, with sea surface temperatures increasing by around 1C in just 2 years. This rapid warming followed a prolonged positive phase of the North Atlantic Oscillation (NAO), but also coincided with an unusually negative NAO index in the winter of 1995/96. By comparing ocean analyses and carefully designed model experiments we show that this rapid warming can be understood as a delayed response to the prolonged positive phase of the NAO, and not simply an instantaneous response to the negative NAO index of 1995/96. Furthermore, we infer that the warming was partly caused by a surge, and subsequent decline, in the Meridional Overturning Circulation and northward heat transport of the Atlantic Ocean. Our results provide persuasive evidence of significant oceanic memory on multi-annual timescales, and are therefore encouraging for the prospects of developing skillful predictions.