In recent years, ocean-based, or marine carbon dioxide removal (mCDR), has rapidly emerged as a promising pathway in the fight against climate change.
In this article – the first instalment in a three part series co-authored by ClimeFi and the World Ocean Council – we explore the science, promise, and commercial momentum behind the pathway today
Why carbon removal – and why the ocean?
As the need to implement credible net zero strategies becomes more urgent, carbon dioxide removal (CDR) technologies are increasingly recognised as essential tools in corporate climate mitigation plans. Companies are turning to durable CDR – technologies that store CO₂ for centuries or longer – in response to growing stakeholder demand for integrity and transparency, as well as its alignment with upcoming regulatory expectations.
To date, most durable CDR purchases have focused on land-based solutions, such as Biomass-based technologies, Direct Air Capture (DAC) or Enhanced Rock Weathering (ERW). However, if we are to meet the IPCC’s target of 10 gigatonnes of removals per annum by 20501, it is increasingly clear that the ocean will also play a central role.
Covering 71% of Earth’s surface and having already absorbed about 30% of anthropogenic CO₂ emissions, the ocean offers immense potential. Meeting the IPCC 2050 target using only mCDR would alter the ocean's dissolved inorganic carbon budget by just 0.007%2.
While ocean-based pathways undoubtedly hold significant potential, the technologies are still relatively nascent. However, growing commercial interest suggests we could be at an inflection point.
What is marine CDR?
mCDR encompasses a suite of ocean-based solutions that aim to durably remove atmospheric CO₂. These technologies – some enhancing the ocean’s natural carbon cycling, others leveraging engineered interventions – either increase oceanic uptake of atmospheric CO₂ or remove previously dissolved carbon resulting in net atmospheric drawdown.
mCDR technologies are commonly categorised as ‘biotic’ (those that rely on biology/photosynthesis) and ‘abiotic’ (those that use physical or chemical ocean processes) or as ‘open systems’ and ‘closed systems’. This article focuses on the latter distinction due to its stronger relevance to near-term commercial viability.
- Open systems: Open systems allow free exchange CO₂ with the ocean or the atmosphere.
- Closed systems: CO₂ sequestration takes place in a closed environment that isolates the CDR process.
Generally, open systems are highly scalable and have lower costs3, while closed systems are more expensive – primarily in terms of upfront investment – but have simpler monitoring, reporting, and verification (MRV).
Over time, it is expected that the MRV costs for open systems will decrease as ocean models improve and projects are able to rely on them. The cost of closed-system projects are also expected to decrease with scale.
The major mCDR pathways
As it stands, there are five major mCDR sub-pathways. Four are open systems, and one is closed:
Each of these different sub-pathways varies in durability, technology readiness level (TRL), and price (see Figure 1)
With each sub-pathway at a different stage of development, where does the pathway stand from a commercial perspective?
Is mCDR attracting buyer interest?
Durable CDR markets are evolving quickly: in 2024, durable CDR purchases surged by 70%, reaching 7.6MtCO₂ removed.
However, despite this growth, only 4% of purchased CDR credits were delivered within the year. This trend indicates that most purchases are strategic offtake agreements, rather than fulfilled deliveries.
To date, only 3.5% of purchased durable CDR volumes are from mCDR (see Figure 2).
However, there are some early signs that the tide might be turning.
In Q1 20254, mCDR recorded its best ever quarter with 230 kt credits purchased, accounting for 33% of total durable CDR purchases. This marked the highest ever amount of mCDR purchased in a single quarter.
A new horizon for carbon removal
While still in its early stages, mCDR has demonstrated strong potential to become a cornerstone of global CDR portfolios.
The innovative approaches outlined, coupled with the increase in commercial uptake in Q1 2025, offer a promising glimpse into a future where the ocean could play a more significant role in carbon removal.
With the groundwork laid, we look forward to bringing you the second article in our three-part series, where we will explore both the challenges and opportunities associated with this nascent but rapidly evolving pathway.
If you have any questions, please feel free to reach out to cdr@climefi.com or jill.storey@oceancouncil.org.
