Take on a podcast episode from The CDR Policy Scoop, originally published Sun, 09 Au. Listen: https://shows.acast.com/the-cdr-policy-scoop/episodes/is-enhanced-rock-weathering-ready-for-scale-with-dirk-paessl

TL;DR

  • Solid-phase and aqueous-phase MRV on the same plot can disagree by orders of magnitude — tons vs kilos of CDR. Not a rounding error.
  • Carbon Drawdown Initiative’s 300-litre buckets have shown zero enhanced-weathering signal after 1,400 days on Furt soil. Publishing the null result matters.
  • ~20,000 credits certified across three geographies via three different solid-phase methods, while Verra declines to write a methodology. That gap is the story.
  • Carbon Plan’s Lithos critique implies ~8.3 tCO₂/ha/yr vs a new Suhrhoff et al. median of ~0.8. 10× is not a discount factor, it’s a different claim.
  • Dirk won’t name a year for ETS-readiness. Mel won’t either. Take that seriously.

Eve Tamme and Sebastian Manhart host Dirk Paessler (Carbon Drawdown Initiative) and geochemist Mel Murphy for a deep-dive on whether enhanced rock weathering (ERW) measurement is anywhere near the rigour policy frameworks like the EU Emissions Trading System or the Carbon Removal Certification Framework will demand. The episode runs long by the show’s standards and earns it.

The load-bearing disclosure: on the “right rock, right soil, right MRV” grid CDI is building (~500 rock/soil combinations in a greenhouse, plus buried mesocosms running past 1,400 days), moving one axis breaks predictions on the other. Same feedstock, different soil, different result. The two dominant measurement families tell divergent stories on the same plot: solid-phase (detrital tracer, total cation accounting, or soil inorganic carbon) integrates a theoretical upper bound of what dissolved; aqueous pore-water gives an instantaneous, often vastly lower flux — and in well-draining sandy soils you sometimes can’t even extract a sample. Murphy: “we’re seeing a difference between tons of CDR with solid phase versus kilos of CDR when we’re looking at aqueous phase.” That is the gap the market is currently pricing through.

The commercial state of play is more awkward than the science warrants. Every one of the ~20,000 certified credits to date used solid-phase quantification, most with a secondary aqueous or gas-flux check. Isometric has now removed the two-method requirement — Murphy notes that across ten projects, not one closed the gap between methods within two standard deviations, so the registry is leaning on conservative discounts instead. Meanwhile Verra says the science isn’t ready. InPlanet’s response — increasing sampling density 10× (1 sample per 20 ha to 1 per 2 ha) between Year 1 and Year 2 credits — is the honest signal here: the operators know the earlier work was undersampled. The Carbon Plan vs Lithos exchange, and Suhrhoff et al.’s preprint median of 0.8 tCO₂/ha/yr, should reset expectations for anyone modelling ERW supply curves at the higher end.

For adjacent context: this pairs well with the Cascade Climate Bedrock Climate Initiative Murphy references (coordinated field sites with comparable MRV), and with earlier CDI writing on the “parking garage” cation-residence-time framing. Paessler’s pitch for data-driven models over process-based ones — plus AEROC’s multispectral field-heterogeneity work to cut the 56% MRV cost share — is where the near-term cost curve actually lives.

Useful for: ERW buyers pressure-testing supplier MRV claims, registry and policy staff calibrating what “ready for ETS” means, and anyone who read the Carbon Plan critique and wants a fair-minded scientist’s read on what happens next.