Abrupt climate change experiments: The role of freshwater, ice sheet and deglacial warming for the Atlantic meridional overturning circulation

• Main Authors: Lohmann, G., Zhang, X., Knorr, G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Deutsche Gesellschaft für Polarforschung; Alfred-Wegener-Institu für Polar- und Meeresforschung 2016
• Subjects: Greenland; Ice Sheet; Polarforschung
• Online Access: https://oceanrep.geomar.de/id/eprint/44245/; https://oceanrep.geomar.de/id/eprint/44245/1/polfor_2016_013.pdf; https://doi.org/10.2312/polfor.2016.013

In this review paper we summarise a series of numerical abrupt climate change experiments in the context deglaciation. The effects of global warming, deglacial freshwater, and ice sheets for the termination of the last ice age are examined in a model of intermediate complexity and a fully coupled, coarse-resolution climate model. We find that gradual deglacial global warming induces an abrupt strengthening of the Atlantic Meridional Overturning Circulation (AMOC). More generally, if the system is in a bistable window, a linear forcing can yield non-linear AMOC changes. In this sense Northern Hemisphere freshwater hosing only modulates the timing of the AMOC onset. Furthermore, Northern Hemisphere freshwater hosing weakens the AMOC with a potential overshoot, after the freshwater forcing has stopped. Therefore, as a further hypothesis the onset of Bølling/Allerød (B/A) interstadial with warming over Greenland could be related to an increase in AMOC, which is induced by a declining freshwater forcing prior to or in parallel with the transition. In contrast, hosing in the Southern Hemisphere has a relatively minor influence on the AMOC. The associated climate signatures and mechanisms are explored and discussed in this study.