Abrupt Atlantic overturning disruptions in warm climates: empirical constraints on future risk

The Atlantic Meridional Overturning Circulation (AMOC) redistributes heat across the globe and sustains the relatively mild climate of Northwest Europe. Ongoing Greenland Ice Sheet melt may weaken the AMOC, yet the risk of abrupt major disruptions remains very uncertain because instrumental records are too short, and models disagree. Past warm climates, on the other hand, provide the only real-world evidence of how the AMOC responds to sustained warming and freshwater input.

Past2Risk introduces a new empirical strategy for assessing AMOC risk by treating past interglacials as natural experiments. We focus on two warm periods with documented AMOC disruptions, MIS 5e (~125,000 years ago) and MIS 11 (~400,000 years ago), and compare them with the Common Era (past 2,000 years), when the AMOC remained stable. Together, these three periods span contrasting climate regimes relevant for evaluating AMOC risk over the coming decades. First, the project will generate high-resolution climate time series over these periods from marine sediment cores across the North Atlantic to reconstruct Greenland meltwater input, deep-water overflow strength near the Faroe Islands, and downstream climate impacts in Scandinavia. Next, we will test whether major AMOC changes were preceded by early-warning signals, or whether substantial weakening can occur without clear statistical precursors. These reconstructions will be integrated with Earth system model simulations (CESM), forced with our empirically constrained freshwater scenarios, to evaluate whether models reproduce the observed thresholds, rates of change, and recovery behaviour.

By grounding model evaluation in geological evidence, Past2Risk provides physically based constraints on how close present-day forcing may be to regimes that previously led to AMOC instability, thus providing an interdisciplinary climate-risk assessment under deep uncertainty.