Captain Drawdown’s daily logbook on every CDR story, paper, and expert voice — so you don’t have to read them all.

Why this matters now

Two things happened in parallel this month. A Nature paper argued that soil and critical-zone processes trap much of the alkalinity enhanced rock weathering (ERW) is supposed to send to the ocean. And Commons and InPlanet announced a distribution deal to sell more ERW credits to more buyers. The measurement debate and the sales channel are moving in opposite directions. If you buy or underwrite these tonnes, you need to understand the argument underneath the invoice.

What is ERW?

Enhanced rock weathering means grinding a reactive rock (usually basalt, sometimes steel slag) and spreading it on farmland. The rock reacts with CO2-rich soil water, forming bicarbonate that is supposed to flow through rivers to the ocean and lock the carbon away for tens of thousands of years. My earlier primer on enhanced weathering walks through the chemistry. The claim sold to buyers is: tonnes of rock in, tonnes of CO2 out, verified by soil sampling and mass balance.

Who’s involved?

The Nature study looked at natural basaltic catchments, finding that critical zone processes limit alkalinity export. The author commentary in Springer Nature Research Communities frames the challenge to ERW directly. The measurement fight itself has been running for over a year. In April 2025, Adam Wolf posted a statistical defense of the Kantola et al. cropland dataset on CDRXIV, responding to a Derry et al. critique. In July 2025, Maxbauer et al. reported a midwestern field trial where steel slag showed CDR but basalt did not. And in June 2025, Suhrhoff et al. published a signal-to-noise analysis of the soil mass balance method that most registries lean on. On the commercial side, Commons and InPlanet just partnered to expand ERW credit distribution.

What just happened?

Steel-manning the critique: if natural basaltic systems, which have had millennia to equilibrate, still retain a large share of alkalinity in soils and secondary minerals, then engineered cropland systems running for a few years face the same physical ceiling. The Suhrhoff paper reinforces this by showing that the mass-balance signal ERW registries rely on is often smaller than the natural variability of the soil column being measured. That is why two competent teams can sample the same field and disagree.

Weighing it honestly: the critique targets the modeled export assumption and the dominant MRV method, not the underlying weathering reaction. The Maxbauer result showing slag working where basalt did not tells you feedstock choice, particle size, and soil chemistry drive real outcomes. ERW is not one product. Treating it as a single line item on a credit portfolio hides where the tonnes actually come from.

Open questions to track

  • Will Isometric, Puro, and other registries update mass-balance guidance to require accounting for critical-zone retention?
  • Will buyers start demanding feedstock-specific quantification (basalt vs. slag vs. wollastonite) instead of pathway-level averages?
  • Does the Wolf-Derry exchange over Kantola et al. resolve, or does the foundational cropland ERW dataset stay contested?
  • How much of already-issued ERW tonnage would survive a stricter signal-to-noise threshold?

Further reading

The market is signing multi-year offtake on a measurement method the literature is actively arguing about. That is the gap. Ask your supplier which side of it their tonnes sit on.

Citations

  1. Nature — finding that critical zone processes limit alkalinity export — research paper
  2. Springernature — author commentary in Springer Nature Research Communities
  3. Cdrxiv — statistical defense of the Kantola et al. cropland dataset
  4. Cdrxiv — midwestern field trial where steel slag showed CDR but basalt did not
  5. Cdrxiv — signal-to-noise analysis of the soil mass balance method
  6. Carbon Herald — Commons and InPlanet just partnered to expand ERW credit distribution