The Atlantic Meridional Overturning Circulation (AMOC) is associated with northward heat transport in the entire Atlantic Ocean, which peaks at 1 PW around 20 N. This ocean heat transport has a long memory and a strong global impact, making the AMOC one of the most important circulation patterns in the climate system. In particular, AMOC variability has been linked to worldwide impacts of high societal cost (including droughts, hurricanes, risk to fisheries and agriculture). A major concern is that the AMOC could be prone to collapse when certain stability thresholds are exceeded. Such a collapse would have dramatic global impacts, with nearly one degree celcius reduction in global mean temperature, and local reductions as high as 12 degrees celcius. The fact that we lack a credible assessment of the proximity of our current (and future) climate to AMOC stability thresholds is a reason for significant concern, and a source of uncertainty for climate projections.

The U.S. Department of Energy (DOE) has invested significant resources in the development of the Energy Exascale Earth System Model (E3SM).  Until, recently the AMOC has been much too weak relative to other models and observational estimates.  While changes to E3SM have improved AMOC, it still remains weak limiting the ability of E3SM to understand and predict changes to AMOC.

In 2022 the DOE's Scientific Discovery through Advanced Computing (SciDAC) program, a partnership between DOE’s Advanced Scientific Computing Research (ASCR) and Biological and Environmental Research (BER) Offices, launched the Improving Projections of AMOC and Collapse Through Advanced Simulations (ImPACTS) project.  The ImPACTS project has two main objectives: 1) increase our physical understanding of AMOC and how it is represented in Earth System Models (ESMs), 2) develop advances in analyses, workflows, and eddy-resolving ESM initialization and efficiency to enable long-term simulations of AMOC and its stability. In the first objective, we will bring together analyses from the ESM and applied math communities to accelerate our analysis capability and transform our understanding of AMOC. While ML/AI analyses for ESM simulations has expanded greatly, none of these analyses have proven transformational. By leveraging the state-of-the-science in AI from the RAPIDS2 institute, we will push the boundaries of AI for ESM analysis. In the second objective, we will utilize recent successes in AI to generate physics-constrained initial conditions at eddy-resolving resolution, allowing us to dramatically reduce the extreme times to achieve ocean equilibration. Improvements in MPAS-ocean model throughput will increase E3SM exascale readiness and has the potential to more than double the performance of the model. Taken together, these improvements will allow us to simulate hundreds of years at eddy-resolving resolution. These two primary objectives will proceed in parallel through most of the proposal but will later combine to deeply probe AMOC strength and its stability across model resolutions, which will be informed by a novel simulation campaign.