Fragmentation of AMOC tipping

Ocean models indicate that the Atlantic Meridional Overturning Circulation (AMOC) may undergo several partial collapses before it fully collapses. Using a conceptual box model, it was recently shown that such fragmentation complicates the interpretation of early-warning signals. Now the question is whether these intermediate transitions survive in models where more detailed processes are represented. A key process here is convection, whose representation can introduce additional branches in the bifurcation diagram, some of which may be spurious. In this commentary, these issues are discussed using conceptual and spatially resolved ocean models, with particular attention to the subpolar gyre. Systematic convergence tests and targeted freshwater-forcing experiments are needed to distinguish robust physical transitions from those caused by insufficient resolution or the mixing formulation. This distinction is important for determining what early-warning signals can tell us about partial and full AMOC collapse.