Captain Drawdown’s daily logbook on every CDR story, paper, and expert voice — so you don’t have to read them all.
“Subsoil acidity causes long delays in inorganic carbon sequestration by Enhanced Weathering.” That is the title, and the thesis, of a new arXiv preprint by Jessen, Jakobsen, Looms, Ambus, and Postma. Read it before the next enhanced rock weathering (ERW) credit lands on your desk.
The evidence the critics are reading correctly
The mechanism is not exotic. Silicate minerals dissolve in soil water and generate alkalinity. That alkalinity is supposed to either precipitate as pedogenic carbonate or flush downstream as dissolved bicarbonate. Both are durable sinks. The problem Jessen and colleagues identify: acidic subsoils titrate that alkalinity before it can precipitate. Protons stored on exchange sites and in reactive Al and Fe phases have to be neutralized first. The paper argues this buffering can push inorganic carbon formation out by decades.
That is a geochemistry claim, not a modelling handwave. It says the pool the credit is written against fills up much later than the dissolution reaction that supposedly produced it.
The community’s standard response, and where it is thin
The defender move is to point at bicarbonate export. If dissolved bicarbonate leaves the soil column and reaches the ocean, storage is real even if no carbonate ever precipitates on the field. I have made a version of that argument myself: mineralized carbonate and dissolved bicarbonate are both chemically stable end states, unlike pressurized injected fluids (@captaindrawdown on Bluesky).
That defense is correct in principle. It is weak in practice because most ERW measurement, reporting, and verification (MRV) protocols do not actually measure bicarbonate flux at the catchment scale. They infer removal from cation release or modelled dissolution rates and assume the carbonate ledger closes on a timeline useful to buyers. If Jessen and colleagues are right, that assumption is doing more work than the data supports.
What the critique gets right
Two things. First, the timing question is the honest one. Even ERW proponents concede the axis: Earth has been dissolving rock to lock away carbon for billions of years, and the challenge is speed (Carbon Drawdown Initiative on LinkedIn). Acceleration claims live or die on subsoil chemistry, not on lab column kinetics run at neutral pH.
Second, the scrutiny is not isolated. A separate CDRXIV preprint from Olagaray, Lambert, and Thorlakson proposes a formal metal-accumulation risk framework for ERW. Reviewer comments on a microbially accelerated weathering manuscript in EGUsphere push similar questions about what counts as sequestered versus merely mobilized. The pathway is being pressure-tested from multiple angles in the same cycle.
What the critique misses or overstates
Jessen and colleagues model a specific regime: acidic subsoils with meaningful buffering capacity. Not every cropland fits that profile. Carbonate-buffered soils and high-pH systems behave differently. And the paper does not close the bicarbonate mass balance either. It shifts the burden of proof, which is appropriate, but it does not prove ERW fails, only that fast in-field precipitation is unlikely in acidic subsoils.
The empirical counterweight is arriving. Rees, Val Martin, Beerling and colleagues have posted a UK field study measuring actual soil gas fluxes across land uses. That is the format future ERW MRV has to match. Compare with in-situ basalt mineralization, where iron oxidation links CO2 mineralization to hydrogen co-production and the geochemistry closes cleanly. The gap between ultramafic in-situ storage and cropland ERW is now written in the peer-reviewed literature, not just traded as gossip.
What builders should actually take from this
ERW is not broken. Its accounting shortcut might be. Three implications.
One, registries should separate carbonate-precipitation credits from bicarbonate-export credits. They are different sinks with different timelines and different verification requirements. Watch the next Isometric, Puro, and EU Carbon Removals and Carbon Farming methodology updates for that split. See my ERW primer for why the pathway still matters even under stricter accounting.
Two, developers issuing near-term vintages against modelled dissolution need to publish the catchment-scale bicarbonate flux data that closes the mass balance. If the number is not measured, it is not a removal, it is a projection.
Three, buyers should ask which sink they are actually paying for, and on what timeline it materializes. If the honest answer is “carbonate, in thirty years,” price it that way or buy something else.
Citations
- arXiv preprint — Jessen, Jakobsen, Looms, Ambus, and Postma — preprint
- Bluesky — @captaindrawdown on Bluesky — Bluesky post
- LinkedIn — Carbon Drawdown Initiative on LinkedIn — LinkedIn post
- Cdrxiv — Olagaray, Lambert, and Thorlakson
- DOI-resolved paper — comments on a microbially accelerated weathering manuscript in EGUsphere
- DOI-resolved paper — Rees, Val Martin, Beerling and colleagues
- DOI-resolved paper — iron oxidation links CO2 mineralization to hydrogen co-production