MRV: The Load-Bearing Wall of a CDR Credit

Measurement, Reporting and Verification (MRV) is the set of procedures a carbon dioxide removal (CDR) project uses to answer three questions: how much CO₂ was actually removed from the atmosphere, how durably it will stay out, and how confident anyone can be in those numbers. It is the load-bearing wall between a project and a saleable credit. If MRV is weak, the credit is uninsurable and, increasingly, unsellable to serious buyers; if MRV is over-engineered, it eats margin that early-stage projects don’t have. Every argument about CDR quality — additionality, durability, leakage, uncertainty deductions — is ultimately an MRV argument.

The measurement families, and why they disagree

CDR MRV pulls from five broad measurement families, and any given pathway usually needs at least two of them stitched together:

  • Direct gas flux — chamber or eddy-covariance measurement of CO₂ exchange between a surface and the atmosphere.
  • Solid-phase / mass balance — weighing carbon in a product (biochar, biomass, mineralised carbonate) and tracking where it goes.
  • Aqueous / pore-water chemistry — measuring alkalinity, dissolved inorganic carbon, or cation fluxes in soil water, rivers, or seawater.
  • Remote sensing — satellite or airborne measurements of biomass, canopy, or surface change.
  • Model-based — process models, life-cycle assessment (LCA), and reservoir simulations that translate proxy measurements into tonnes.

These families disagree, often severely, on the same plot of land. Enhanced rock weathering is the sharpest example. If you measure solid-phase depletion of applied basalt or olivine — cations lost from the grain — you typically infer tonnes of CO₂ per hectare drawn down. If you measure the aqueous phase — bicarbonate and cation export in pore water or drainage — you often see kilograms. The discrepancy comes from secondary carbonate precipitation, cation exchange on clays, biomass uptake, and slow transport to the ocean, all of which decouple the solid-side “potential” from the aqueous-side “realised” removal. Similar wedges appear in soil carbon (bulk-density and depth assumptions swing results by multiples) and in ocean CDR, where a National Academies research strategy for ocean-based CDR explicitly flagged verification as the binding constraint on the entire pathway.

The point is not that one family is right. It is that MRV must specify which family is authoritative, what the others are used for, and how the gap is booked as uncertainty. LCA compounds the problem: a critical review of LCA for CDR technologies found system boundaries, counterfactuals, and biogenic-carbon accounting choices routinely change results by an order of magnitude on identical technologies.

How it bites by pathway

Biochar has the tractable end of MRV: pyrolysis produces a solid whose mass, carbon content, and H/C ratio (a durability proxy) can be measured on site. Producers like NetZero, Bio-Logical, Dark Earth Carbon and Alcom Carbon Markets issue under registries (Puro.earth, Verra, Isometric) that require lab characterisation, feedstock tracking, and application records. The unresolved parts are downstream: how much of the applied biochar’s carbon persists over 100+ years across soil types, and how to book the priming and yield effects that a systematic review of 26 biochar meta-analyses and the Nature Communications synthesis on biochar climate mitigation both show are highly context-dependent.

Direct Air Capture (DAC) has the opposite problem: the capture itself is metered like a chemical plant — mass-flow controllers, CO₂ purity, injection volumes — so gross removal by operators such as Climeworks, Heirloom, Skytree or CarbonCapture Inc. is metrologically boring. The MRV fight is entirely on the LCA side: grid emissions, sorbent manufacture, and (for mineral-loop systems) calcination fuel. Net tonnes, not gross, are what a buyer pays for.

bioenergy with carbon capture and storage (BECCS) projects like Svante/Carbon Alpha, Reverion, and Carbon America must merge industrial flue-gas metering with upstream biomass counterfactuals — the question “would this biomass have decayed, burned, or grown back?” is not a measurement, it’s a model, and the answer sets the credit volume.

Nature-based programs — Grow Indigo’s smallholder soil-carbon work, Klim’s regenerative platform, Green Carbon’s forestry — depend heavily on remote sensing plus sparse ground truth, with permanence discounts that can consume a large fraction of gross tonnes.

Registries have moved in response. Isometric publishes pathway-specific protocols with explicit uncertainty deductions; Puro.earth revised its biochar methodology to tighten feedstock and durability rules; Verra’s VM0044 for enhanced weathering has been iterated as the solid-vs-aqueous debate has sharpened. The direction of travel is fewer default values, more direct measurement, and larger conservative deductions when models are used in place of measurements.

The hard parts

MRV cost is the most cited number in private and the least cited in public: for early-stage novel CDR, verification, monitoring, and third-party auditing routinely run into the double-digit percentages of project cost, and higher for small projects like The New Black Biochar or Carbon Remove that cannot amortise a monitoring rig over millions of tonnes. Three questions remain genuinely open. First, how long durability must be demonstrated ex ante versus monitored ex post — a governance question about what “net zero” even means, laid out in Fankhauser et al.’s “meaning of net zero”. Second, how to converge solid-, aqueous-, and model-based estimates in weathering and ocean pathways without either double-counting or writing off real removals. Third, who pays for long-tail monitoring once a project developer has been paid and moved on. Until those are settled, MRV is not a technical afterthought — it is the product.