Weaker ocean circulation could cost trillions

A weakening of the North Atlantic overturning circulation would cause the ocean to absorb less carbon dioxide - this is associated with economic costs and the climate continues to heat up

In Brief

• High follow-up costs: A weakening of the North Atlantic Meridional Overturning Circulation (AMOC) could cause follow-up costs of several trillion euros by the year 2100, as less carbon dioxide is absorbed by the ocean and the climate continues to heat up.
• Correction of the data: Research shows that previous studies have likely underestimated the consequences of AMOC mitigation, which could lead to more frequent and extreme weather events.
• Combination of different modelling: The results are based on a global climate model and economic modelling that calculate the consequential costs of climate damage due to rising CO₂ levels in the atmosphere.

The North Atlantic Meridional Overturning Circulation (AMOC) transports warm water north from the Tropics and cold water back to the south, serving as a “radiator” for Europe’s climate. Until recently, economic research has considered a weakening AMOC to be beneficial, as this would cool the Northern Hemisphere in periods of global warming. “But a weakening AMOC would further accelerate climate change”, explains co-author and climate economist Felix Schaumann, Ph.D. candidate in Sustainability Economics at the University of Hamburg (UHH) and the Max Planck Institute for Meteorology (MPI-M).

The CO₂ content of the atmosphere is increasing

What we already knew: When the Arctic ice melts, massive amounts of freshwater flow into the ocean. The seawater becomes diluted and less saline, a development that reduces its density and causes it to sink more slowly – and one that will likely slow the AMOC. The ocean is also the largest carbon sink on Earth. It absorbs more carbon than the atmosphere and terrestrial organisms. The cold waters of the Arctic Ocean are particularly receptive. Now, Schaumann and his colleague Eduardo Alastrué de Asenjo (UHH and MPI-M) have confirmed: as a result of this process, less CO₂ is transported from the surface ocean to the deep ocean. More CO₂ remains in the atmosphere, accelerating global warming.

Global heating continues

In global terms, the acceleration of climate change would produce more frequent and extreme weather events like heat waves, droughts and floods, leading to an increase in the social cost of carbon. This cost represents the damage caused by additional CO₂ emissions, and the increase in the social cost of carbon could offset the economic benefits of the cooling that accompanies a weaker AMOC.

The social cost of carbon

The findings are based on a global climate model in combination with an economic model that estimates economic costs along different scenarios of CO₂ emissions. Using this approach, the experts created a first scenario based on the CO₂ development without any AMOC-related effects, and a second, which reflected various degrees of weakening. This allowed them to establish a direct connection between the strength of the AMOC and the amount of carbon the global ocean can take up.