The AMOC is a key component of the climate system, responsible for ocean heat and freshwater transport, associated with the ventilation of anthropogenic carbon, and anticipated to experience or drive climate tipping points. Due to its identification as a potential tipping element in the climate system–a process which, through incremental perturbation, can be forced into a qualitatively different state–it has received substantial attention. From paleo-records, it has been deduced that the AMOC has the potential to rapidly switch between an “on” state with a strong overturning circulation, and an “off” state with a weak or absent circulation, where these switches between on and off states have been used to explain glacial-interglacial cycles.
The concern now is that in a warming climate, the remaining northern hemisphere ice sheets or the intensification of the hydrological cycle could input sufficient freshwater to the North Atlantic to slow or shutdown the AMOC. The subsequent reorganisation of the climate system following a shutdown of the AMOC could be dramatic, resulting in changing distributions of mean and variable temperatures and weather patterns across Europe and beyond. While the IPCC report in 2021 (chapter 9) indicated high confidence that the AMOC will decline in the 21st century, there is low confidence in the magnitude of the decline and only medium confidence that it will not collapse by 2100. Simultaneously, the IPCC assessment reduced confidence (from medium to low confidence) in whether the AMOC is already declining, citing missing key processes in numerical simulations used to predict future AMOC evolution.
Against this backdrop, EPOC outcomes are anticipated to deepen our process-level understanding of this complex circulation system and contribute to assessment of past AMOC change and future evolution. The project uses multi-observational consistent approaches to diagnose AMOC variability since 1993, and re-evaluation of paleo-proxies for AMOC variability since 1950. EPOC employs high-resolution coupled climate models with grid spacing roughly 10 times finer than standard models, testing the expectation that finer resolution can reduce model biases and increase confidence in AMOC representation.
Beyond contributing to assessments, EPOC works towards a more sustainable next-generation AMOC observing system. Many recent advances in understanding the AMOC and identifying missing processes in climate models are due to observing efforts since 2000; however, the system has not been optimised and represents substantial investments by multiple international programmes. Through modelling and observing tests, EPOC will recommend a future AMOC observing system across the whole Atlantic, incorporating next-generation technologies where appropriate.
