
🪨 Back to one of my favourite, often heatedly debated topics. This time, the authors Hamed Sanei, Henrik I. Petersen, David Chiaramonti, and Ondrej Masek take aim at how “two pool decay models” have been used in biochar permanence research.
🔬 This common approach is used among others by the frequently referenced Dominic Woolf study (2021) which forms the basis for permanence decay functions in most biochar carbon removal (hashtag#BCR) standards, including the IPCC.
😱 The TL;DR: Woolf and others massively underestimate the permanence of BCR.
More precisely, the authors highlight two key concerns in their peer-reviewed study:
1️⃣ The use of a two pool model, but only in theory, given the split between labile fraction (<1% - C1) vs recalcitrant fraction (>99% - C2), de-facto using a one-pool model, and then grossly overestimating the decay function of C1 over C2.
📉 The authors go as far as saying that “The division of biochar carbon into C1 and C2 pools in Woolf’s model was primarily undertaken to facilitate curve fitting, with the objective of achieving the closest fit to the empirical data for carbon decay observed over time during the incubation experiments”.
2️⃣ They suggest a disconnect between the current model and underlying biochar chemistry. In conventional models such as Woolf’s, assumptions are made on the % of recalcitrant fractions (C2) based on things like pyrolysis temperature. However, these are just approximate and shown to be far from reality.
🔎 The authors conclude that, “this discrepancy undermines the validity of the model, as proper parameterization of a decay model must be rooted in a robust understanding of the chemical processes governing carbon degradation and stability.”
🤷 So where to go from here? Should we completely ditch two pool decay models? Not entirely. A multi-pool model based on the actual chemical composition of biochar, measured through (for example) reflectance rate testing, could still be used and yield accurate results.
🔨 Summing up, this is a pretty damning take on an approach that still seems to dominate biochar permanence standards globally. I am curious to see what debate this will unleash and whether this turns out to be the nail in the coffin for what seems to be an outdated approach. See comments for the latest BCR permanence science we should probably reference instead.
🧐 What is your take? Is this a fair analysis or did the authors miss something?
Comments