In their new article, our partner Fondation Tara Ocean discusses the risks and uncertainties linked to marine geoengineering.
As the climate crisis accelerates, the Ocean is increasingly put into the spotlight. Covering more than 70% of the Earth’s surface, it absorbs around a quarter of human‑generated CO₂ each year. This natural capacity has sparked many discussions on “blue carbon” solutions and large‑scale marine geoengineering. But while these ideas promise rapid climate benefits, scientists warn that they may create more problems than they solve.
Coastal ecosystems such as mangroves, seagrass meadows and salt marshes play an essential role in the global carbon cycle. Through photosynthesis, they capture CO₂ and store it in biomass and sediments. Yet, these ecosystems are among the most threatened on the planet and when degraded or destroyed, they release their stored carbon back into the atmosphere.
Plankton, often overlooked in climate discussions, captures as much carbon annually as all the world’s forests. Most of this carbon is recycled in surface waters, but a small fraction sinks to the deep ocean, where it can remain for centuries. This “biological pump” is essential to climate stability, yet it is now being reframed as a potential tool for engineered carbon removal, an assumption that simplifies a complex system.
A number of marine geoengineering solutions are being suggested in global debates, such as:
- Ocean fertilisation to stimulate phytoplankton growth.
- Alkalisation to increase CO₂ absorption.
- Artificial upwelling to bring nutrient‑rich deep water to the surface.
- Direct injection of CO₂ into deep waters or geological formations for storage.
- Biological control of harmful algal blooms (HABs).
- Permanent carbon sequestration through the cooling of surface water.
In theory, these techniques promise large‑scale carbon sequestration but, in practice, they carry profound ecological risks ranging from nutrient imbalances to ocean acidification. Therefore, applying the precautionary principle is essential.
To explore the full analysis and recommendations, access the original article and policy brief from the Fondation Tara Ocean.