Weakening AMOC reduces ocean carbon uptake and increases the social cost of carbon

Direct link to the paper: DOI: 10.1073/pnas.2419543122

Abstract
A weakening of the Atlantic Meridional Overturning Circulation (AMOC) has been found to be globally beneficial by economic assessments. This result emerges because AMOC weakening would cool the Northern Hemisphere, thereby reducing expected climate damages and decreasing estimates of the global social cost of carbon dioxide (SCC). There are, however, many other impacts of AMOC weakening that are not yet taken into account. Here, we add a second impact channel by quantifying the effects of AMOC weakening on ocean carbon uptake, using biogeochemically-only coupled freshwater hosing simulations in the MPI-ESM Earth system model. Our simulations reveal an approximately linear relationship between AMOC strength and carbon uptake reductions, constituting a carbon cycle feedback that leads to higher atmospheric CO2 concentrations and stronger global warming. This AMOC carbon feedback, when incorporated into an integrated climate-economy model, leads to additional economic damages of several trillion US dollars and raises the SCC by about 1%. The SCC increase is similar in magnitude, but of opposite sign, to the SCC effect of Northern Hemisphere cooling. While there are many other potentially relevant economic impact channels, the AMOC carbon feedback alone could thus flip the consequences of AMOC weakening into a net cost to society.

Audio summary

🎙️ Here’s two artificial podcast hosts summarising the paper (credit: NotebookLM)

Two corrections to the audio summary:

1️⃣ By 2100, we project 4-12 GtC, not 15 GtC (the 15 GtC figure comes from our ESM run which assumes very drastic weakening, not from our projections).

2️⃣ The Northern Hemisphere cooling is not a short-term process, it’s also a long-term benefit and its economic impact is in the same order of magnitude as the economic impact of the AMOC carbon feedback.

Recommended citation: Schaumann, F., Alastrué de Asenjo, E. (2025). "Weakening AMOC reduces ocean carbon uptake and increases the social cost of carbon." PNAS. 122(9).