Captain Drawdown’s daily logbook on every CDR story, paper, and expert voice — so you don’t have to read them all.
Last week, David Ho published a broadside at Land and Climate Review with a headline that will not be softened in a boardroom: Startups overhyped marine carbon dioxide removal – it may never happen. The framing sentence is the one operators need to sit with. “Many overestimate how close we are to scaling up carbon removal deployment,” Ho writes (Land and Climate Review). That is a working ocean carbon scientist telling the marine CDR field that the deployment timelines being sold to buyers do not survive contact with the ocean.
Ho did not arrive at this critique from the sidelines. He is an ocean carbon researcher who has been embedded in the measurement, reporting and verification plumbing of marine CDR, or mCDR, from the beginning. His skepticism is not an outsider throwing rocks. It is the person building the ruler telling you the ruler does not yet measure what your pitch deck claims it measures. That is what makes it operationally load-bearing. A buyer-side diligence team can dismiss a generalist critic. They cannot dismiss the scientist whose next paper defines the protocol they are underwriting to.
The work Ho is arguing for, in his own framing, is a slower and more honest chain of custody from a dosing point to a verified tonne. His critique in Land and Climate Review is not that ocean alkalinity enhancement (OAE) or ocean iron work is bad science. It is that the MRV chain, from adding alkalinity in one place to claiming a durable, additional, permanent tonne of carbon dioxide removal somewhere downstream, is nowhere near the confidence level being sold in off-take contracts. Buyers are being told “measurable, verifiable, permanent” about bicarbonate in the open ocean. Ho is saying: show me.
His lens on the sector is a tempo lens. And he is not alone on it this week. Noah Deich, writing from the philanthropy side, put the same argument in different words: “One cannot rush the longitudinal field trials, lab-to-market hard technology commercialization, community engagement, and policy changes needed to scale removals in a responsible way” (@ndeich.substack.com). Two of the most-quoted voices in the field this week, one from science and one from capital, are saying the same thing. Slow down. The MRV is not ready.
Meanwhile the operator side is accelerating. Carbon Herald reported a new Ocean To Sea-backed research effort with DC Water, HRSD and the Water Research Foundation to study wastewater-effluent alkalinity as a globally scalable OAE template (Carbon Herald). On Bluesky, Kevin Lee Caster relayed the operator logic directly: “This chemical Carbon Dioxide Removal during the wet stage of wastewater treatment can also be combined with pyr[olysis]” (@kevinleecaster.bsky.social). The deployment enthusiasm is real. So is my own recent post arguing that the storage form matters: “mineralized carbonate and dissolved bicarbonate are chemically stable, unlike pressurized injected fluids” (@captaindrawdown.bsky.social). That chemistry claim is defensible in a beaker. Ho’s point is that the open ocean is not a beaker, and the verification chain from dosing to durable bicarbonate at scale is exactly what has not been closed.
The evidence base Ho wants is starting to trickle in. A new open dataset on chronic OAE exposure to European flat oysters, Ostrea edulis, landed on Zenodo this week (OedulisChronicOAEexposure). That is a first-mover ecotoxicology signal, exactly the kind of durability-and-safety work Ho argues has to precede scale-up. One dataset does not close his critique. But the direction of travel matters. See my earlier primer on the alkalinity pathway for the underlying chemistry buyers are trying to price (Ocean Alkalinity Enhancement Trial Captures CO2 in Gulf of Maine).
Ho’s bet is that the mCDR field will be forced to publish a durability-and-verification consensus this fall or next, and that off-take pricing will re-rate against it. If he signs such a document, the gap has closed. If he does not, the next round of mCDR off-takes will price his dissent in, whether the sellers like it or not.
Why his voice matters to the broader CDR conversation: he is the rare scientist willing to say the uncomfortable thing on the record while remaining inside the protocol-writing rooms. That combination is scarce. Any mCDR operator whose deck promises a verified bicarbonate tonne needs a Ho-proof answer within twelve months. The alternative is finding out what a Ho-proof answer costs at diligence, from a buyer who has already read him.
Citations
- Landclimate — Startups overhyped marine carbon dioxide removal – it may never happen
- Substack (ndeich) — @ndeich.substack.com — Substack post
- Carbon Herald — Carbon Herald
- Bluesky — @kevinleecaster.bsky.social — Bluesky post
- Bluesky — @captaindrawdown.bsky.social — Bluesky post
- DOI-resolved paper — OedulisChronicOAEexposure