There is an ongoing debate among scientists regarding the potential collapse or slowdown of the AMOC. Both scientific support and contrasting views can be found among colleagues at the Bjerknes Centre for Climate Research. In this new episode of the Bjerknes Climate Podcast, host Stephen Outten discusses these two viewpoints with Andreas Born and Marius Årthun.
Earlier this autumn, Professor Andreas Born signed a letter with 45 other scientists calling for more research into the AMOC and an assessment of the risks for Nordic countries. You can read the letter here.
Andreas Born is a professor at the Institute for Earth Sciences at the University of Bergen (UiB) and works on the dynamics of the climate system, with a focus on the Atlantic Ocean and Northern Hemisphere ice sheets, as well as a keen interest in paleoclimate research.
In his scientific work, Born uses, modifies, and develops numerical models across a range of complexities—from simple box models to comprehensive coupled global climate models. He also leads the strategic research project Dynasor at the Bjerknes Centre, which aims to deepen our understanding of the North Atlantic circulation.
Also present in the podcast studio is Marius Årthun, research leader for Climate Hazards at the Bjerknes Centre for Climate Research.
Årthun is an expert in large-scale oceanography in the North Atlantic and Nordic Seas. He works on the predictability of climate variations and has previously combined observations and fieldwork with numerical models. Årthun has recently published a paper suggesting a strengthening in parts of the AMOC, challenging the notion of its overall weakening.
In this episode, the three scientists discuss what the AMOC is, potential disruptions, current research, and future predictions.
The podcast aims to be a discussion among scientists, not focused to be in a pop-sci language.
Understanding the AMOC
The AMOC is a complex system of currents that brings warm water northwards over the Atlantic Ocean. As this water approaches higher latitudes, it cools and sinks, creating a cycle that is essential for the Earth's climate. This process is driven by the Earth's rotation and wind patterns, making a complete collapse unlikely as long as these fundamental forces persist.
Potential Disruptions
The main concern surrounding the AMOC is the possibility of its slowdown or partial shutdown. This could occur due to the disruption of the cooling and sinking process, primarily through the addition of freshwater to the Atlantic. The Greenland ice sheet is a significant source of such freshwater, which, being less dense than saltwater, could form a "lid" on the ocean surface, potentially hindering the sinking of cooler water.
Current Research and Predictions
Recent models used by the Intergovernmental Panel on Climate Change (IPCC) suggest a decrease in AMOC strength of 30-50% by the end of the century. While this doesn't constitute a complete collapse, it represents a significant reduction. The IPCC report published in 2023 states with medium confidence that the AMOC will not collapse within the year 2100, with the likelihood being below 10%.
While climate models are the most advanced tools available for assessing future possibilities, they have limitations. They struggle to accurately represent certain processes, such as undercurrents and the sinking of water. Some scientists argue that these models may be inherently too stable, potentially underestimating the risk of AMOC instability.
Real-world observations over the past 20 years show significant variability in the AMOC, but the time series is not long enough to definitively conclude whether it is weakening or not. The complexity of the AMOC system and the limitations of current models make it a challenging subject to predict with certainty.