Recent research suggests that increasing seawater alkalinity by tens of millimoles per liter could theoretically enable the ocean to absorb several gigatonnes of CO₂ annually. This prospect has sparked debate around geoengineering as a potential 'miracle solution' for offsetting industrial emissions. However, scientists emphasize that implementing this at a local scale carries major uncertainties, both chemically and ecologically. The article published in Nature Climate Change explores the limits of this mechanism using high-resolution simulations and satellite observations. At its core is a series of predictive models combining neural networks and atmospheric data to evaluate potential sequestration gains and associated risks.
The study's findings: Absorption capacities and limits
The authors indicate that if alkalinity were increased by 30 mmol L-1 in coastal zones, the ocean could theoretically remove several gigatonnes of CO₂ annually, a figure that appears impressive on a global scale. However, this potential is strongly dependent on location: cold waters rich in nutrients absorb more than already carbon-saturated tropical regions. Moreover, increasing alkalinity promotes calcium carbonate precipitation, which can alter seafloor chemistry and impact calcifying organisms.
When these figures are scaled down to the level of a local community, gains are notably more modest. Pilot experiments described in the study, conducted in protected bays, showed measurable reduction in atmospheric CO₂, but far from the global scale gigatonnes. Prediction uncertainty remains high, particularly because local biogeochemical processes are poorly characterized and current models do not always capture small-scale ecological feedbacks.