A new paper in Communications Earth & Environment used formal expert elicitation to estimate how much CO₂ enhanced rock weathering (EW) on agricultural land could actually remove. The headline number: 0.2–0.7 Gt CO₂e/yr on average, depending on the feedstock — but with a wild range from below zero to above 5 Gt CO₂e/yr.

The kicker? Only 27–39% of the potential CDR is actually realized. The rest gets lost along the way — through secondary clay formation, calcite saturation, deep soil processes, and freshwater emissions.

What they did

The authors — Buma, Dietzen, Gordon, and colleagues — ran a structured expert elicitation with specialists across EW science. They assessed six different feedstocks and asked experts to quantify both the CDR potential and the uncertainties in the loss pathways from field to ocean.

This isn’t a model study. It’s a calibrated snapshot of what the people closest to the science actually think.

Key findings

  • Feedstock matters enormously. Wollastonite scored highest for CDR potential but faces severe supply constraints. Basalt is more available but less efficient.
  • The field-to-ocean pathway leaks. Calcite saturation, secondary mineral formation, and soil carbon interactions all eat into the theoretical CDR.
  • 27–39% efficiency means for every tonne of rock you spread, you realize roughly a third of the theoretical CO₂ removal.
  • Data gaps are real. Experts flagged deep soil processes and freshwater emission pathways as the biggest unknowns.

Why this matters

EW is already being deployed commercially — companies are spreading crushed rock on farmland right now. But the science is still catching up with the deployment. This paper is an honest reckoning: EW has genuine gigatonne-scale potential, but the efficiency losses are substantial and poorly understood.

For the MRV community, this reinforces what CDI has been saying: carbon-based MRV alone isn’t enough for field EW. You need cation-based approaches and multi-year monitoring to capture what’s really happening.

The paper doesn’t kill EW’s promise — it quantifies the gap between promise and delivery. That’s exactly the kind of honesty this field needs.

Source: Buma et al. (2026), Communications Earth & Environment

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