No, Collecting Seafloor Metals Won't Wreck the Ocean Carbon Cycle

In mid-June, John Oliver aired a segment on Last Week Tonight condemning proposals for deep sea mining, in this case investigating efforts to use underwater robots to collect potato-sized metals-rich polymetallic nodules from the seabed. While characteristically entertaining, Oliver’s critique repeated several exaggerations commonly circulated by opponents of seafloor nodule collection—exaggerations that in reality greatly contradict our scientific understanding of ocean science and marine life.

Urging the public to scrutinize nodule collection’s potential environmental impacts is as understandable as it is beneficial for promoting oversight and accountability. Indeed, civil society ought to act as a measured counterbalance to a nodule collection industry, pushing companies to improve practices and enjoining the International Seabed Authority (ISA) and national agencies to tightly enforce regulatory standards.

However, such public engagement is only constructive insofar as it remains committed to evidence and analysis. In going as far as to claim that seafloor nodule collection in the Clarion-Clipperton Zone (CCZ) could threaten the ocean’s ability to store carbon dioxide, for example, both John Oliver and the activists who supplied him with that argument stray from grounded debate into unscientific point-scoring. In general, it appears that Last Week Tonight simply accepted many common counterarguments against seafloor nodule collection at face value, rather than interrogating those claims or statistics more closely.

At any reasonably imaginable scale of seafloor nodule harvesting, the ocean carbon sink will experience effectively zero impacts. Numerous other claims that Oliver makes throughout his segment also contain clear inaccuracies that warrant correction or discussion. Unpacking such statements helps promote more nuanced, evidence-based assessments of the potential benefits and costs of nodule collection, including how innovative regulations or technology can help improve that balance further.

Given the significant advantages nodules could offer—critical minerals for the energy transition sourced far from human communities with fewer carbon emissions, less excavation, and more international regulatory accountability—a more rational public conversation can only benefit people and the planet.

Claim: “...the ocean actually absorbs about a third of all the carbon dioxide we produce. In fact, a type of bacteria found in the CCZ a few years ago was found to be taking up large amounts of carbon dioxide and could be playing an important part of the deep-sea carbon cycle.”

Correction: It is the surface ocean that is responsible for absorbing atmospheric CO2 through air-sea gas exchange. A combination of surface ocean physical, chemical, and biological processes convert those dissolved carbon dioxide molecules into other forms of carbon and/or transfer carbon to the deep ocean, where carbon cycles very slowly and resides for thousands of years. This cycling of carbon between the surface ocean and deeper waters operates at unfathomable scales—100 billion metric tons of carbon in both directions annually.

Such processes utterly and inconceivably dwarf the negligible carbon captured and released by animals and bacteria on the abyssal seafloor. Insofar as seafloor organisms are remotely meaningful to deep ocean carbon cycling, this stems from the sum of their collective small-scale activities across the planet-spanning abyssal deep. And while certain regions like the North Atlantic Ocean and the waters surrounding Antarctica are important regions for ocean carbon cycling, oceanographers do not particularly count the Clarion-Clipperton Zone among them. To imply that seafloor fauna in the Clarion-Clipperton nodule field determine the fate of the ocean carbon sink is a remarkable claim that, if taken seriously, would revolutionize the entire discipline of ocean carbon biogeochemistry.

While John Oliver focused primarily on the erroneous idea that seafloor nodule collection could disturb immense quantities of ocean carbon, a more realistic and minor concern exists that pumping deep ocean nodules and water to the surface could release some CO2 by giving CO2-rich deep ocean waters the opportunity to interact with the atmosphere. However, the nodule-collecting ship would pump these waters back down to the deep ocean almost immediately, denying them the considerable time they would have to remain at the ocean’s surface to fully discharge their CO2 surplus.

While some CO2 would still escape, these amounts may still be small relative to the fossil fuels needed to mine the same metals on land—a question well within the ability of scientists to answer with further study. In any event, such CO2 releases are negligibly tiny compared to the titanic disruptions of ocean carbon that Oliver and some activists have implied would result from seafloor ecosystem impacts.

Claim: “...more than 80% of the world’s oceans remain unexplored and unmapped.”

Correction: This claim requires additional context. The global oceanographic community has already fully mapped Earth’s seafloor at 1.5 kilometer resolution, and oceanographers have now mapped 24.9% of the seafloor to an even higher resolution of 100 meters, with international scientific efforts well underway to map the remainder by around 2030. In fact, many areas of the Clarion-Clipperton Zone, including the Belgian and German exploration zones, have contributed high-quality data to these very efforts, making this region relatively well-surveyed.

In any event, detailed topographic data is of limited use for comprehensively assessing potential environmental impacts from a given project, whether it is on land or on the seabed. This is why environmental impact assessments, such as those required by the ISA to secure permits for commercial nodule collection, require extensive baseline study of the relevant areas, their surroundings, and the wildlife and habitat contained therein. Invoking statistics on global bathymetric mapping to argue insufficient knowledge of the relevant seafloor region thus represents somewhat of a non-sequitur.

Claim: “[The ISA] hasn’t given out any exploitation licenses to actually commercially mine the ocean floor yet, but it’s given out dozens of so-called exploratory licenses which are the first step toward doing that…. Wow, a zero percent rejection rate? It’s not ideal that the body responsible for something as important as protecting the deep sea has lower standards than the University of Phoenix.”

Correction: Despite their disclaimer, John Oliver and his staff do not sufficiently clarify the difference between exploration licenses and licenses for commercial-scale exploitation. For seafloor nodules, the ISA has issued 19 exploration contracts for small-scale surveying and testing with the strict requirement that contractors cannot sell any minerals collected. Such initial trials pose relatively minimal environmental risks, and one would therefore expect the ISA to rarely reject an exploration license application outright.

Time will tell whether the ISA’s judgment regarding any future exploitation contracts enforces sufficiently strong standards, but in any event the stringency of environmental review for commercial-scale exploitation will undoubtedly be considerably higher than the threshold of due diligence required to conduct mapping and pilot testing. This is the case for terrestrial mineral exploration on land, where test drilling and surveying in countries like the United States typically does not require a full review, with agencies like the Bureau of Land Management only evaluating notices of exploration activities for regulatory compliance and completeness. Thus, the ISA’s lack of rejected exploration license applications relative to the 19 licenses granted to date is not particularly compelling evidence that the ISA is grossly neglecting its duties as an international regulatory body.

Claim: “....during this process, [collector vehicles] will also collect about 5 to 30 centimeters of sediment from the seafloor.”

Correction: Oliver’s segment included clips from an interview featuring this remark by marine biologist Dr. Diva Amon, which suggests an upper range of seafloor sediment disturbance that goes beyond what prospective nodule operators, other marine scientists, or even NGO watchdog groups claim could result from nodule collection activities. Many operators maintain based on testing that their collector vehicle designs will not disrupt more than the top 5 centimeters of sediment. NGO groups themselves often publish materials suggesting impacts as deep as 10 centimeters. Much scientific work cites a range of between 5-15 centimeters.

The cut depth of collector vehicles is an empirical question that researchers can clearly evaluate given sufficient testing. But at any rate, the claim that collector vehicles could disturb sediment to depths of 15 to 30 centimeters goes well beyond the range of values cited in most ongoing discussions, and requires further substantiation.

Claim: “...the unwanted sediment and seawater from the cleaning process will be released back into the ocean. And that could either happen close to the seafloor or at much shallower depths closer to the surface.”

Correction: This statement from Dr. Amon also requires clarification. “Much shallower depths closer to the surface” might imply release of return water as close as 500m or 1000m below the surface. In practice however, many operators are committing to release return water at depths between 2000m and all the way down to the seafloor itself, based on whatever depth minimizes environmental impacts. This is well below the upper 1000m of the ocean where the overwhelmingly vast majority of open ocean biomass lives.

Such return water releases will also be far more dilute than the shown computer-rendered video suggests. One initial paper based on pilot testing suggests that return water from a full-scale commercial operation would dissipate to a dilution factor of 1:40,000 within just several kilometers of the release point, while producing additional seabed sedimentation on the order of just 1% of natural sedimentation rates. Further testing and environmental impact assessment can evaluate the robustness of such findings, while regulators can determine and mandate the standards for return water release necessary to best assure environmental protection.

Some early-stage collector vehicle concepts even propose lifting nodules to the surface using hoppers or containers, which would in theory eliminate the need to discharge return water entirely. Such intriguing approaches deserve further investigation and development, but remain to be demonstrated and economically proven.

Claim: “While it is true that the metals inside them are a key component of batteries now, lithium-ion batteries are fast being replaced by new battery chemistries that don’t require cobalt or nickel.”

Correction: This is perhaps an overstatement of current battery technology trends. The advance of nickel and cobalt-free lithium-iron-phosphate (LFP) and lithium-manganese-iron-phosphate (LMFP) batteries in recent years has now partially decoupled electric vehicle and battery production from demand for nickel and cobalt battery cathode materials. However, nickel-based battery cathode chemistry still accounted for 60% of the global lithium-ion battery market in 2023, and the International Energy Agency projects that nickel-based chemistries will continue to account for at least 40% of the battery market by 2040. Given as much as tenfold growth in electric vehicles and fifteen-fold growth in electricity grid battery storage by 2030 in IEA modeling that assumes aggressive global climate policies, this means that global demand for battery-grade nickel and cobalt will in all probability continue to rise for the foreseeable future.

Why might nickel-based chemistries like nickel-manganese-cobalt (NMC) persist to such a degree? Currently, NMC batteries still boast the best electricity storage capacity for a given battery weight, making them desirable for applications like long-range electric vehicles, freight trucks, electric shipping, and electric aviation. Future technological shifts could yet change this calculus, but new battery designs will require a long time to develop and enter the commercial market.

In the video, John Oliver spotlights sodium-ion batteries, correctly noting that this battery type doesn’t require nickel, cobalt, manganese, or even lithium. But sodium-ion batteries’ primary weakness is their low energy density, while their advantages include long lifetimes and low cost, making them most competitive in grid storage applications, which will likely account for only 10%-20% of future global total battery capacity across the transportation and power sectors combined.

What kind of discussion on seafloor nodules will most benefit society?

The above quotes represent the most clearly misleading technical and regulatory points from Oliver’s segment that warrant some clarification. Other claims John Oliver made are somewhat more fair.

Collector vehicles would leave long-term impacts on the seabed, not least of all by permanently removing the nodules themselves from the ocean floor. The extent to which sediment ejected from collector robots creates bottom plumes that harm marine life also deserves further study, even if preliminary results suggest plumes remain confined to a limited vertical and horizontal extent. Technological advances, good regulatory standards, and careful environmental impact assessments could considerably ameliorate such effects, acknowledging that operators will never be able to mitigate them entirely. Indeed, as management plans for the CCZ have progressed, the ISA has already designated 31% of the CCZ for conservation in perpetuity.

Perhaps the most fair point John Oliver raises is that some low and middle-income countries sponsoring aspiring operators in the CCZ seem to be receiving relatively low royalty fees per unit of nodules collected, on the order of 0.5% the total value of the harvested metals. While Oliver did not mention that those countries will also benefit from the regulatory and license fees they mandate from partner companies, sponsoring countries like Nauru, Tonga, Jamaica, or Kiribati perhaps do deserve to negotiate for higher royalties from future nodule collection given their pressing development needs.

All of which is to say that many questions around nodule collection—both scientific and regulatory—offer many options for resolution. Society will benefit most from discussion based on specific, scientific, evidence-based claims around potential and measured impacts, and vigorous debate over the best approaches to regulate such impacts while fairly distributing the economic benefits from any seabed commercial activities.

Promulgating outdated or misleading claims is ultimately not just counterproductive to such efforts, but self-defeating for environmentalists’ own efforts to remain credible within those discussions. Above all, such messaging clashes with the professed veneration of and respect for science at the heart of not only much of the current opposition to nodule collection proposals, but within mainstream environmentalism in general. Of all people, John Oliver, as an outspoken advocate for progressive, rational, and evidence-based politics, ought to show greater commitment to facts over flair.