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Marine carbon dioxide removal (mCDR) is getting increasing attention. Often overlooked, the ocean’s vast capacity to store CO₂ is now seen as a vital climate lever, and one with distinct advantages over land-based carbon removal.

This second article in a three-part series by ClimeFi and the World Ocean Council explores the emerging opportunity in ocean-based CDR and the challenges still to overcome.

Ocean-Scale

The oceans already absorb 30% of human CO₂ emissions and store over 50 times more carbon than the atmosphere. Unlike land-based CDR, ocean-based methods avoid conflict with agriculture and urban development.

From seaweed farming to electrochemical CO₂ removal, many mCDR solutions can operate offshore or near coastal infrastructure, avoiding the physical constraints of terrestrial CDR.

More Than Carbon: Ecosystem Co-Benefits

Many mCDR approaches also deliver ecological benefits, such as reducing ocean acidification and improving habitats for species like corals and shellfish. These impacts support marine biodiversity and help restore fisheries.

Yet trade-offs remain. Electrochemical methods can raise pH levels but may introduce trace metals like nickel. Nutrient-based approaches may trigger harmful algal blooms or disrupt marine food webs. Ongoing research is working to minimize these impacts.

MRV: The Measurement Challenge

Robust measurement, reporting, and verification (MRV) remains a major barrier. Ocean dynamics make it harder to quantify carbon removal than in closed terrestrial systems.

Still, progress is underway:

• Puro.earth has opened a protocol consultation for microalgae-based sinking.
  
• Isometric published its DOCS protocol.
  
• Nonprofits like Carbon-to-Sea and SeaO2-CDR are building foundational science and standards.

Marine CDR is following a familiar arc, similar to enhanced rock weathering, where early MRV difficulties are now giving way to verified crediting.

Regulatory Friction

Permitting mCDR projects is complex and often slow. Many jurisdictions lack clear frameworks for these new technologies, leading to delays that are especially risky for startups with limited funding runways.

But regulation can also be an enabler. Existing ocean discharge regulations can be adapted, and co-locating with industries like desalination or wastewater treatment (e.g. Captura’s system) can help navigate existing permitting channels.

What’s Needed Next

mCDR is gaining momentum, but scaling it requires more than science. A stronger demand signal — backed by policy, buyers, and procurement frameworks — is essential to unlock investment.

Encouragingly, MRV tools are improving, regulation is catching up, and community engagement is growing. With the right safeguards, marine CDR could become a key tool not only for carbon removal, but also for ocean restoration, thus making mCDR a viable part within CDR portfolio management and construction.

Upcoming in the ClimeFi mCDR Series: The next article will look at real-world mCDR deployments and speak with early buyers and suppliers helping shape this growing market.

In other carbon removal news, Syncraft opens high altitude climate positive Power Plant in the Swiss Alps.