Evaluating the risk of tipping cascades through the strength of the bipolar seesaw

The potential for the coupling between tipping elements leading to the occurrence of tipping cascades is of deep concern. One major tipping cascade that is often invoked results from coupling between the Greenland ice sheet, the Atlantic meridional overturning circulation (AMOC) and the Antarctic Ice Sheet (AIS). Melting of Greenland could contribute to a weakening of the AMOC, which would then result in a decrease in the northward heat transport in the Atlantic Ocean, causing warming of the Southern Ocean around Antarctica. This idea is supported by the evidence provided by ice-core records and models of different complexity suggesting that, during the last glacial period, the Southern Ocean acted as a heat reservoir which dampened and integrated in time the North Atlantic abrupt climatic variations through the bipolar seesaw. However, it has been argued instead that the heat reservoir to the Atlantic meridional heat transport involved does not lie in the Southern Ocean but north of the Antarctic Circumpolar Current, and transmitted via the atmosphere to the interior of Antarctica. Determining the ultimate heat reservoir in the sense of the strength of the Southern Ocean heat reservoir is critical to evaluate the risk of a tipping cascade.  Here we will investigate how model resolution affects the strength of the bipolar seesaw and the ultimate heat reservoir involved in this mechanism by using two different model horizontal resolution versions (0.25 and 1 degree, respectively) of the HadGEM3-GC3-1 model in simulations with a reduced AMOC in response to freshwater forcing in the North Atlantic.