By Dr. Sophie Gill • Dr. Jing He • Dr. Jennifer Yin

There is scientific consensus that in order to stay below 2° C of warming by 2100 and to mitigate the worst effects of climate change, we need to rapidly reduce emissions, as well as develop technologies that can remove billions of tonnes of carbon dioxide from the atmosphere each year.

There is a wide range of emerging carbon dioxide removal (CDR) technologies, a subset of which utilizes the ocean for carbon removal and storage. These marine CDR (mCDR) approaches are a particularly promising class of CDR technologies with extremely high scaling potential because they leverage the vast surface area and large carbon storage capacity of the ocean. The ocean naturally contains about 40 times more carbon than the atmosphere and already absorbs about a quarter of human-made carbon dioxide emissions. Various mCDR approaches aim to enhance the ocean’s ability to absorb carbon dioxide.

The Science and Technology

Most mCDR approaches seek to reduce the partial pressure of dissolved carbon dioxide in the surface ocean, which prompts the surface ocean to re-equilibrate with the atmosphere and absorb more carbon dioxide from air. The removed atmospheric carbon is then durably stored for more than 10,000 years in the ocean.

mCDR approaches can be broadly categorized into those that leverage biological processes and/or organic materials (biotic) and those that do not (abiotic). Biotic mCDR approaches aim to increase the growth of micro- or macroalgae and enhance the storage of organic carbon in the deep ocean via sinking. When these marine plants grow, they take up the dissolved carbon dioxide in the ocean through photosynthesis. In contrast, abiotic mCDR approaches include ocean alkalinity enhancement (OAE) or direct ocean capture (DOC), which reduces the amount of carbon dioxide in the ocean by leveraging the ocean’s natural chemistry, or through direct extraction of seawater carbon dioxide.

The Market

Five years ago, the landscape for mCDR was mainly academic, with markets nascent for these technologies. Since then, we’ve seen a significant increase in the number of mCDR companies working on R&D for a variety of biotic and abiotic approaches, as well as an increase in public and private investment. For example, mCDR companies have been the recipients of advance market commitments from the Frontier buyer group, orders from the first round of carbon removal purchases from the U.S. Department of Energy, and finalists in the Carbon Removal XPRIZE. There have also been significant increases in research funding for mCDR from the U.S. and EU, as well as from private philanthropic organizations, such as the Carbon to Sea Initiative.

The use of carbon credits, where one credit represents 1 tonne of carbon dioxide removed from the atmosphere, creates economic incentives for the development and scaling of mCDR projects. In order to generate trustworthy carbon credits, it is important that CDR projects carefully quantify their removals through scientifically rigorous measurements and models and transparently report their data for verification by an independent third-party organization. Collectively, this process is known as measurement, reporting and verification (MRV).

Thus, in addition to developing the science and technology to carry out the mCDR activity, it is just as important to develop the necessary MRV science, technology and infrastructure to successfully scale mCDR. This will require an all hands on deck approach, with the need for more ocean sensors, measurements, models and data analysis tools.

With the rise of all this recent activity in mCDR, there is a need for clarity and guidance on what constitutes as a “high-quality” marine carbon removal credit. This is traditionally the role of a carbon removal registry, which can be thought of as a public ledger for carbon removal projects that have passed that registry’s quality bar and have gone through an independent third-party verification process.

Registries develop MRV protocols, which are rulebooks that carbon removal companies must follow when carrying out their activities and quantifying their carbon removals to ensure the credits issued are scientifically sound. High-quality and scientifically rigorous protocols are essential for instilling confidence that a carbon removal credit is actually a net benefit to the climate and to prevent greenwashing. Building this trust is essential to growing the mCDR market and advancing technologies to help achieve global climate targets.

Isometric’s Advancements

In May 2024, Isometric became the first carbon registry to publish a protocol for marine carbon removal through ocean alkalinity enhancement. The protocol, authored by ocean scientists at Isometric, details how OAE projects—which increase the ocean’s natural ability to draw down and store atmospheric carbon dioxide—can quantify their removals based on the best available science.

The Isometric OAE Protocol requires both measurements at the original project site as well as the use of internationally recognized numerical ocean models to quantify additional drawdown of carbon into the ocean. The quantification methods used in this protocol have been informed by Isometric’s research partnership with [C]Worthy, a leading research organization that is building open-source software tools to support MRV of mCDR projects. This rigorous approach to MRV is critical to instilling confidence for buyers of mCDR credits.

The first project developer who has signed up to this protocol is Planetary Technologies. Planetary Technologies adds naturally abundant alkaline minerals to coastal water systems to deliver alkalinity to the ocean and facilitate additional carbon drawdown. Shopify, MaRS and Terraset are some of the first buyers of credits from Planetary that will be delivered against the Isometric OAE Protocol.

All Isometric protocols are developed in line with the Isometric Standard, which is the world’s most robust set of rules for carbon removal. This protocol was created in collaboration between Isometric’s in-house science team and interdisciplinary expert reviewers in biogeochemical ocean modeling and chemical, biological, and ecological responses to OAE, and field trial researchers. It also underwent review within the Isometric Science Network, a group of more than 200 carbon removal scientists. This holistic approach is critical to ensuring the best available science is shared among industry, academic and research organizations.

So, what’s next for us at Isometric? We’re excited to start seeing some early deployments working with our MRV protocol for OAE, and we’re working on protocols for other mCDR approaches, such as electrolytic seawater mineralization and direct ocean capture. We are excited to continue building confidence in how we can leverage the best available science to responsibly learn from early mCDR deployments and help scale this important set of technologies.

Dr. Sophie Gill holds a Ph.D. in carbon removal from the University of Oxford. She previously worked as a CDR consultant for Stripe (Frontier), Carbon XPRIZE, CEA Consulting and ClimateWorks. She is the marine carbon removal manager at Isometric.

Dr. Jing He is a carbon removal scientist at Isometric and leads the research partnership with [C]worthy. She earned her Ph.D. at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. Her experience includes conducting a global modeling study of ocean alkalinity enhancement at Google’s Climate & Energy team.

Dr. Jennifer Yin is a carbon removal scientist at Isometric who earned her Ph.D. at Stanford in coastal ocean physics and observations. She is an expert in building and deploying measurement systems in the natural environment. Yin worked previously at Jupiter Intelligence, GE and IBM.

Caption: Schematic of the four spatio-temporal regimes that need to be characterized to calculate gross CO₂ removal, from Isometric’s Ocean Alkalinity Enhancement from Coastal Outfalls protocol. (Credit: Isometric)