Tipping of the Atlantic Ocean Circulation

The Atlantic Ocean Circulation, in particular its zonally averaged component called the Atlantic Meridional Overturning Circulation (AMOC), is one of the tipping elements in the climate system. The AMOC is sensitive to freshwater perturbations and may undergo a transition to a climate disrupting state within a few decades under continuing greenhouse gas emissions. The potential climate impacts of such a collapse are enormous and hence reliable estimates of the probability of its occurrence before the year 2100, central within TAOC, are crucial information for policy makers. There are several important challenges to provide such estimates of transition probabilities, to determine the climate impacts of an AMOC collapse and to predict the occurrence of such an event. We will develop novel computational methodology to determine transition probabilities between equilibrium states in a hierarchy of climate models, which is the computational challenge in TAOC. Application of these techniques will lead to estimates of AMOC transition probabilities versus observable quantities and to transition paths, being the climate dynamics challenge in TAOC. The climate modeling challenge in TAOC is to simulate an AMOC collapse in one of the state-of-the-art climate models under at least one scenario of climate change. Finally, a skillful prediction scheme for future AMOC behavior will be developed, using traditional and novel observable precursors based on transition paths, which is the climate prediction challenge in TAOC. TAOC will advance the field of climate dynamics by providing (i) novel computational techniques to study probabilities of tipping phenomena in a hierarchy of climate models and (ii) novel scientific knowledge on the vulnerability of the AMOC under future climate change.