Marine geoengineering will not save the oceans or the climate

Life on Earth would not exist without the oceans and their interconnected and fragile ecosystems, many of which we barely understand. In addition to providing livelihoods for billions of people, marine ecosystems serve as the planet’s lungs, producing roughly 50% of the oxygen we breathe, while absorbing 30% of greenhouse-gas (GHG) emissions and nearly all the associated excess heat. As the legendary oceanographer Sylvia Earle succinctly put it: “No water, no life. No blue, no green.”
But over the past few decades, the world’s oceans have been under massive pressure from climate change, pollution, habitat destruction, acidification, and overfishing. And these fragile ecosystems now face a new threat: high-risk attempts to manipulate the oceans through technological interventions. These efforts, collectively known as marine geoengineering, could exacerbate human-caused ocean degradation, thereby jeopardising our planet’s life-support systems. To protect ocean health, citizens and scientists worldwide must urge policymakers to restrict these technologies.
Marine geoengineering – encompassing techniques like seeding the ocean with iron to stimulate the growth of carbon-absorbing phytoplankton and increasing the reflectivity of clouds by spraying them with saltwater mist – is often touted by its proponents as a potential solution to climate change. Tellingly, however, none of these approaches tackle the root cause of climate change: fossil fuels. And, in fact, major polluters and big business are already investing in these interventions as a ploy to maintain their usual practices.
In reality, marine-geoengineering technologies will not work, cannot be scaled, or are so dangerous that they should never be deployed. Consider, for example, ocean liming. This technique aims to increase the ocean’s ability to absorb carbon dioxide by adding large quantities of alkaline substances to the ocean.
One analysis suggests that liming the ocean at the scale required to make a dent in atmospheric CO2 levels would necessitate the use of nearly all the active large ships in the world. Given that most ships are powered by fossil fuels, the resulting GHG emissions alone would render the effort self-defeating.
Moreover, obtaining the necessary amounts of alkaline substances would mean a significant expansion of the highly polluting mining industry. One estimate suggests that achieving this would require 3,000 terawatt hours of electricity and an additional 10bn tonnes of processed rock, surpassing the total production of the global coal-mining industry over the past 250 years.
While it is well established that ocean acidification threatens marine life, the biological and ecological impacts of ocean liming are not well understood but are likely to be just as harmful. Rapid changes in the chemical makeup of water would likely harm or kill species that have evolved to live in stable and specific environmental conditions. The introduction and unpredictable spread of mineral particles would contaminate the water, block sunlight, and suffocate plankton and other marine organisms, thereby disrupting the biological carbon pump that is crucial to storing CO2 in the deep ocean.
Marine cloud brightening, which involves pumping seawater into the atmosphere to increase cloud reflectivity, is another geoengineering technique that poses significant risks. At scale, it would likely shift rainfall and monsoon patterns, thereby potentially exacerbating droughts and hurricanes. Marine ecosystems could be severely affected by increased salt deposits on the sea surface, slowing carbon absorption and reducing light levels and ocean temperatures. If implemented at scale, marine cloud brightening could not be quickly stopped because the shock of termination would result in a sudden increase in temperatures, leading to unforeseeable and potentially catastrophic consequences.
Against this backdrop, the recent decision by the California town of Alameda to refuse to host a marine-cloud-brightening experiment is a welcome development. This decision reflects growing public and governmental awareness of the dangers posed by these technologies, even in their infancy. It should serve as a model for other cities, states, and countries.
With our oceans under increasing strain, we must combat all forms of marine pollution. As the International Tribunal for the Law of the Sea declared in a landmark judgment in May, this includes GHGs. But we cannot geoengineer our way out of the climate crisis. Marine-geoengineering technologies essentially aim to replace one form of pollution – CO2 – with another, in clear violation of the UN Convention on the Law of the Sea. In doing so, they distract us from the urgent need to phase out fossil fuels.
Alarmingly, international institutions appear ill-equipped to slow the development and commercialisation of marine geoengineering, even though a de facto moratorium on these technologies has been in place under the UN Convention on Biological Diversity since 2010.
The need for effective global regulation was reiterated by the parties to the London Protocol in an October 2023 statement that recognised the ability of marine-geoengineering technologies to cause “deleterious effects that are widespread, long-lasting, or severe” and warned against their deployment.
Attempts to monetise marine carbon-removal technologies even before their effectiveness and impacts can be established are another cause for concern. Companies and startups in this emerging field are already selling carbon credits, thereby prioritising profit over precaution. Worse, some of these startups are financially supported by fossil-fuel companies.
Oceans are humanity’s greatest allies in the fight against climate change. We cannot afford to manipulate these vital and complex ecosystems, especially when doing so would distract us from the urgent imperative of phasing out fossil fuels. To protect the ecosystems that sustain all life on Earth, we must restrict marine-geoengineering experiments and prevent these technologies from being deployed. – Project Syndicate
l Lili Fuhr is Director of the Fossil Economy Program at the Center for International Environmental Law. James Kerry, Senior Marine and Climate Scientist at OceanCare, is an adjunct senior research fellow at James Cook University.