Ready…or not? Carbon Dioxide Removal as an Ocean-based Climate Solution

By Sarah Cooley and Anna-Marie Laura

The sum total of all the climate commitments made to date put the planet on track to warm 2.7°C by 2100.  As it becomes more and more likely that we will overshoot the Paris Agreement greenhouse gas emissions target to limit planetary warming by 2100 to only 1.5 or 2°C, there is increasing interest in tinkering with Earth’s natural processes to increase uptake of carbon dioxide (CO₂) and remove it from the atmosphere—commonly referred to as carbon dioxide removal (CDR). All the future scenarios that meet, but don’t go over, the Paris Agreement temperature target include both swiftly cutting present-day greenhouse gas emissions and CDR.

In the last few years, interest has exploded in ocean CDR, a collection of techniques that leverage the ocean’s biological, physical and geochemical processes to take up extra atmospheric CO₂. The ocean looks like an attractive site for carbon removal—it’s a lot bigger, with a lot fewer people (for sure!), than most places eligible for land-based CDR. Compared to land-based CDR, ocean CDR is complicated further by the ocean’s circulation, which carries perturbations both through deep basins and across political boundaries to nearby and faraway ecosystems that might respond in hard-to-predict ways. And there is also the challenge of working in a physically and logistically harsh environment. Ocean CDR is a relatively young research area with much left to discover. Research is still needed on the potential effectiveness of different techniques to sequester CO₂, as well as on ocean CDR’s potential effects on biodiversity or social equity—like whether ocean CDR techniques could alter the ocean food chain or set new standards on effective, inclusive environmental decision-making.

Some of the ocean CDR methods being advanced by researchers and investors. Not shown is restoration of marine ecosystems and large marine animal biomass, which has also been proposed. © RITA ERVEN/GEOMAR

In December, 2021, the National Academies of Science, Engineering, and Medicine released a new report, “A Research Strategy for Ocean Carbon Dioxide Removal and Sequestration.” It identifies the most urgent research questions about ocean CDR and sketches out a research program to answer them, considering a range of approaches from electrochemistry to restoring marine life and ecosystems. The report reviews what is known about these approaches from existing laboratory or small-scale experiments as well as insights borrowed from carbon-cycle models six decades in the making. The report notes that we still need to understand the intended and unintended impacts of interventions, including how they interact with other important ocean ecosystem services and human activities. We also need to understand the cradle-to-grave emission levels associated with CDR techniques to make sure they actually capture the CO₂ as intended, whether they are scalable, and what controls and safeguards are appropriate.

One way to support a coordinated, complex body of research on ocean CDR that also minimizes risk is to develop a code of conduct for the field. The need for a code of conduct is a main conclusion of another report, also released in December, 2021, from the Aspen Institute titled “Guidance for Ocean-Based Carbon Dioxide Removal.” No matter what, research coordination and transparency will help make the most of public and private investments already happening in ocean CDR. But a code of conduct will help accomplish this as well as minimize the risk of unintended harmful consequences of research at larger scales while uncovering the needed information on the full scope of environmental and social outcomes of ocean CDR. Ultimately, multidisciplinary research scaffolded by a code of conduct will support comparing ocean CDR methods fairly with other climate change actions to best support evidence-based decision making about ocean-based carbon removal.

It’s already clear that CDR would need to be a complement, not a substitute, for rapid, ambitious emissions cuts. Some ocean-based climate mitigation solutions are being deployed now to reduce emissions, such as expanding well-sited offshore wind energy and reducing maritime shipping emissions. The benefits and risks of newer ideas like ocean CDR still need to be understood. Fortunately, ocean CDR research is at an early enough stage that the community can still gather evidence, utilize inclusive methodologies, understand different points of view and explore alternatives. Solving the climate crisis is too important to double down on solutions that don’t work the way we hope or that wreak havoc on the people and ecosystems we’re trying to protect. Investing in a solid research agenda for this solution set is our best bet to get it right.