Permanence Debates
Chapter on open scientific and policy debates about biochar permanence: decay-model form, inertinite/Ro claims, horizon choice, and what “permanent” should mean for CDR accounting. Complements the settled mechanism snapshot in Permanence and the proxy chapters. Report context: 2026-09-16.
Related notes: Consensus vs Debates · Permanence Science for Credits · Reflectance Ro and HyPy · Woolf IPCC Fperm · Risks and Controversies · Science Hub · Key Sources
1. What is largely settled
- Well-made biochar (adequate T / low H/C_org) persists far longer than raw biomass; fused aromatics are the mechanistic basis (reviews biochar climate mitigation · DOI).
- Persistence is probabilistic and environment-dependent, not literal immortality (Schmidt et al. 2025; models soil GHG from biochar · DOI).
- Inventory practice can use mass × (F_C) × (F_\mathrm{perm}) with kiln/gate MRV (CDR Potential and IPCC Accounting).
2. Debate A — Do short incubations overestimate long-term decay?
Claim: Two-pool fits from incubations lasting only a few years may mis-estimate (often overestimate) millennial decay of the recalcitrant pool, because the “slow” pool is still a mixture and true inert fractions need other assays (HyPy, Ro, conductivity) (frontier discussion in science report 2026-09-14; Azzi et al. 2024 modelling work listed in Key Sources · DOI).
Counterweight: Woolf/IPCC deliberately use ≥1-year multi-pool fits and conservative exclusions (no priming credit, mineral soils only) so inventory factors are less likely to over-credit (Woolf 2021; IPCC PDF).
Vault posture: Active research—not settled. Prefer transparent horizon + method; cross-check high-permanence marketing claims against Reflectance Ro and HyPy and Schmidt policy commentary.
3. Debate B — Decomposition-model camp vs inertinite/Ro camp
| Camp | Core tools | Typical horizons | Exemplars |
|---|---|---|---|
| Decomposition-model | Multi-pool decay, H/C_org, T-class, soil T | 100y (IPCC/Woolf); “several centuries” / 200y in some markets | estimates soil C stock change from biochar, models soil GHG from biochar, Puro CORC200+, Isometric 200y |
| Inertinite / Ro | Random reflectance, HyPy-resistant C | Millennial / “permanent” upper classes | inertinite permanence benchmark, Isometric 1000y, CSI upper class |
inertinite permanence benchmark IBRo2% (Ro = 2%) and modelled ~100 Myr half-life under stated oxidizing conditions (DOI) energize the Ro camp. Schmidt et al. 2025 push back: do not equate modern biochar with geological inertinite; refuse 100% permanence declarations; recommend policy definitions on the order of centuries with registered material properties, traceable application, conservative modelling, and long-term field validation.
Puro’s public permanence post (2025-07-03) explicitly chose centuries not millennia pending more integrated science (puro.earth permanence post)—a market illustration of Debate B, detailed on the credit side in Permanence Science for Credits / Puro CORC200+.
4. Debate C — Which time horizon is “the” permanence number?
UNFCCC GWP practice and IPCC biochar appendix center 100 years (IPCC PDF; Woolf discussion of GWP analogy DOI). Woolf also publishes 500- and 1000-year factors showing large further losses (e.g. high-T at 14.9 °C: 0.82 → 0.25 from 100y to 1000y — Table 3).
Choosing 100y vs 1000y changes both the number and the narrative. Neither is wrong if labeled; mixing them in marketing is.
5. Debate D — Climate feedback and non-soil uses
- Warming feedback: higher future soil T lowers (F_\mathrm{perm}) (Soil Temperature and Environment).
- Non-soil matrices (concrete, asphalt, polymers): oxygen/microbe exposure differs; soil (F_\mathrm{perm}) tables do not automatically transfer (Materials and Built Uses, Consensus vs Debates).
6. How this vault talks about permanence
- Lead with mechanism + proxies + (F_\mathrm{perm}) chapters, not slogans.
- Cross-link markets via Permanence Science for Credits without pasting registry tables into science notes.
- Flag Lehmann H/C < 0.5 subset figures as full-text not re-checked (reviews biochar climate mitigation).
- Align with Schmidt 2025 on rejecting absolute millennial zero-decay claims unless a specific protocol’s evidence bar is met and disclosed.
Primary links
- Schmidt et al. 2025
- Sanei et al. 2024 · inertinite permanence benchmark
- Woolf et al. 2021 · models soil GHG from biochar
- IPCC 2019 App. 4
- Azzi et al. 2024
- Puro permanence post