The pitfalls of sourcing biomass for carbon removal

The attraction is real before the problems start. Plants photosynthesize on the order of 400 gigatons of CO2 a year, enough that the Northern Hemisphere growing season shows up as a seasonal wobble in the global CO2 record. Almost all of that carbon returns to the atmosphere through respiration, decay and consumption, so biomass-based removal is an attempt to intercept some of the return trip. The engineering ladder runs from burying wood in a clay pit, through biochar, a charcoal-like form made by heating biomass without oxygen, up to bioenergy with carbon capture and storage. All are cheaper and more scalable than building machines to do the same work, and all need feedstock, which is where the difficulty moves. Across every proposed use of biomass in a 2050 bioeconomy, from aviation fuel to lumber to paper to carbon removal, the best estimates Cabiyo has seen put potential demand at 11 to 16 times sustainable supply. That fact reorganizes everything else, and it is why he points to cascading use: send a scarce resource to its best and highest use, recycle it down the chain, and only combust it with capture at the end.

Which is what breaks the industry’s favorite defense. Projects almost always claim to be using waste, and Cabiyo says that in each of the bad cases he has seen, the label was attached to material that was not. His example is the largest pellet producer in the world, which claimed to run on sawmill residues, treetops and branches. The trouble is that pelletization needs high-quality material; you cannot make good pellets from that mix, you need whole logs. So whole logs is what got sourced, including saw logs that would otherwise have become lumber. But the deeper objection is structural rather than empirical. Even honest waste is temporary, because at an 11-to-16-fold supply gap somebody will find a use for it, and that is already visible: Cabiyo describes a project sourcing a pile of logs everyone assumed would be burned, until another buyer turned up wanting them for pallets. He is careful not to overclaim, granting that a burn pile in a forest arguably is waste right now. What matters is the accounting rather than the semantics. If the material was genuinely going to burn, the carbon math is easy and the claim is clean. Take that away and you have to estimate what would otherwise have happened, which is where the honesty of the whole enterprise now sits.

Two kinds of harm follow, and they do not collapse into each other. One is the carbon math, where Kann puts the logic plainly and Cabiyo agrees: if you did nothing to reduce demand for everything else wood is used for, diverting a log into energy means one more tree gets cut somewhere and the removal claim evaporates. The other is social and environmental harm, which survives even when the carbon math works: harvesting old growth or high-conservation-value forest, operating where land tenure is contested or Indigenous land rights are disputed, and the local burden of the supply chain itself, since pellet mills are loud and dusty and have to be sited somewhere. Neither speaker pretends these go to zero. Kann’s framing is that there is no free lunch in decarbonization and the question is what is acceptable, with visibility into the trade-off. Cabiyo’s is that some lines are easy, such as not feeding old growth into a boiler, while weighing a community’s attachment to a maturing forest against the climate value of harvesting it has no clean answer at all.

The sharpest analytical move in the episode is about scale, and it cuts against both sides of the usual argument. Zoom in to a single harvested plot and any bioenergy-with-capture project looks terrible: the stand is clear cut, standing carbon is low, and regrowth takes decades, so the payback period is long. Cabiyo says that is true, that it is the lens most critics use, and that it is the wrong scale. Zoom out to the globe and forest carbon stocks are stable or rising, partly from CO2 fertilization, so anything looks carbon neutral and you could justify cutting whatever you like. Also the wrong scale. The report lands in between, at an ecologically defined region perhaps the size of a small US state, where patches of harvest and regrowth coexist and you can ask whether stocks there are stable or increasing. Pressed by Kann on why the global view fails, Cabiyo concedes he has no clean answer and calls it an active debate, then offers the one he has: at global resolution a genuine local decline is invisible and cannot be attributed to the facility causing it. Gigatons, as he puts it, are made of megatons, and the math has to be done where the damage would show. The same instinct produces the report’s interim rule against market distortion: biomass should be a genuine byproduct of a harvest, not its main product.