Have you ever heard of marine geoengineering? Probably not, yet hundreds of companies are already experimenting with techniques to transform the oceans into giant CO2 vacuum cleaners. The idea sounds great: instead of reducing emissions, we chemically manipulate the seas to absorb more carbon dioxide. A billion-dollar business that promises to save the climate without much effort.
It's a pity that a new German study published in Environmental Research Letters just turned the tables, revealing that these technologies could accelerate the death of the oceans.
Marine Geoengineering: When the Cure Becomes Worse than the Disease
Marine geoengineering works with a seemingly simple logic: If the oceans already naturally absorb 25% of our CO2 emissions, why not help them do more? The techniques being tested range from fertilization with iron to stimulate the growth of plankton, cultivation of huge kelp forests, Fine ataddition of alkaline minerals to alter marine chemistry.
Andreas Oschlies and his team of GEOMAR Helmholtz Center have analyzed these methodologies with global climate models, discovering a disturbing side effect. Many of these techniques, especially the biological ones, could dramatically accelerate oxygen loss in the oceans. The mechanism is perverse: by stimulating the growth of marine biomass, a decomposition process is then triggered that consumes precious oxygen.
The Lost Oxygen Paradox
The numbers from the German study are merciless. Marine geoengineering could cause a loss of dissolved oxygen between 4 and 40 times greater than the expected benefits from reducing global warming. It's like emptying a swimming pool just to fill a glass.
The oceans have already lost about 2% of their oxygen in the last fifty years due to global warming. Warm water holds less oxygen, and this phenomenon is creating more and more “dead zones” where marine life simply cannot survive. As I pointed out in this article, ocean acidification is already a ticking time bomb for marine ecosystems.
Marine Geoengineering: The Most Dangerous Techniques
La ocean fertilization with iron It is one of the riskiest methodologies. The idea is simple: spread iron in the sea to stimulate the growth of phytoplankton, which should absorb more CO2. The problem? When these microorganisms die, they sink and decompose in a process that devours oxygen and can create extensive hypoxic zones.
Macroalgae cultivation presents similar risks. Companies such as Seafields design sea farms of 95.000 square kilometers in the Atlantic, an area as large as Portugal. But if this biomass sinks and decomposes, could deprive vast areas of ocean of vital oxygen.
The carbon credit business
Behind the explosion of marine geoengineering is a rapidly growing market: carbon credits. Companies can sell “tokens” representing tons of CO2 removed from the atmosphere, each worth hundreds of dollars. Over 2024 marine credits were sold in 340.000, compared to just 2.000 four years ago.
The risk is that the race for profit is pushing experiments on an ever-increasing scale without adequate environmental assessments. As he warns Robert Danovaro of the Polytechnic University of Marche, one of the 13 marine biologists who raised the alarm on Science: “The proposed projects are mostly still in a theoretical, model-based phase.”
Is there a safe road?
Not all is lost. The study identifies some geochemical techniques, such as alkalinization of the oceans obtained with calcareous minerals, which appear to have minimal impacts on oxygen levels. These methodologies do not stimulate biological growth, thus avoiding the perverse cycle of growth-decomposition-oxygen consumption.
The cultivation of macroalgae with active biomass harvesting appears particularly promising. If we harvest the algae instead of letting them sink, we can avoid underwater decomposition. According to the models, This technique could even restore up to 10 times the oxygen lost due to climate change.
The lesson to be learned
Marine geoengineering teaches us a fundamental lesson: There are no magic solutions in climate. Every intervention has consequences, often unpredictable. As Oschlies points out: “What helps the climate is not automatically good for the ocean.”
Instead of looking for technological shortcuts, perhaps we should focus on the simplest and safest solution: stop burning fossil fuels. The seas have enough problems without us turning them into guinea pigs for planetary experiments.
