Bioenergy with carbon capture and storage — BECCS — is the IPCC’s workhorse. It appears in the vast majority of net-zero pathways. Climate models lean on it to close the gap between what emissions reductions can achieve and what the atmosphere actually needs. It’s supposed to be the technology that makes the math work.
A new preprint from researchers at Princeton University, the University of Hong Kong, and the World Resources Institute says the math might be wrong.
The Core Problem: Carbon Debt
Their finding is stark: BECCS is “likely to produce higher emissions for decades than natural gas without carbon capture.”
How is that possible for a technology that’s supposed to remove carbon?
The answer lies in carbon debt — the time lag between when biomass is harvested and when new growth reabsorbs the same amount of CO₂. When you burn a tree for energy (even if you capture the smokestack CO₂), you release carbon that took decades to accumulate. The replacement tree won’t recapture that carbon for another 40-100 years, depending on the species and growing conditions.
During that gap, the atmosphere sees a net increase in CO₂. And if you’re comparing BECCS to natural gas without capture, the biomass route can actually be worse — because the upfront carbon release from biomass harvesting exceeds the fossil emissions it’s supposed to replace.
Why This Matters for Net-Zero Models
The IPCC’s Sixth Assessment Report includes BECCS in nearly every pathway that limits warming to 1.5°C or 2°C. Some scenarios assume 5-10 gigatons of CO₂ removal per year from BECCS by 2050 — numbers that dwarf every other CDR method combined.
If those projections carry a decades-long carbon debt that models don’t fully account for, the climate math changes dramatically. We might be planning to remove carbon that we first emitted by deploying the removal technology itself.
This isn’t a new concern. Scientists have debated biomass carbon accounting for years. The EU’s Renewable Energy Directive treats biomass as carbon-neutral at the smokestack — a simplification that critics have long challenged. What’s new here is the direct comparison to unabated fossil fuels, and the blunt conclusion that BECCS could be worse than doing nothing for decades.
Not All BECCS Is Equal
Context matters. The researchers focused on woody biomass — the kind of BECCS that involves harvesting forests or using wood pellets. Agricultural residues, purpose-grown energy crops, and waste biomass have different carbon debt profiles. A BECCS plant running on sawmill waste or sugarcane bagasse doesn’t carry the same multi-decade regrowth penalty as one burning whole trees.
The problem is that most large-scale BECCS proposals involve woody biomass, because that’s where the volumes are. The Drax power station in the UK — the world’s largest BECCS pilot — runs primarily on wood pellets, many imported from North American forests.
What This Means for CDR
This preprint doesn’t kill BECCS as a concept. But it does three things:
Demands better accounting. Carbon debt needs to be reflected in lifecycle assessments, not assumed away. When and how the carbon comes back matters as much as whether it comes back at all.
Challenges model assumptions. If IPCC pathways are built on BECCS delivering net-negative emissions from day one, and the reality involves decades of net-positive emissions first, those pathways need revision.
Strengthens the case for other CDR methods. Direct air capture, enhanced weathering, biochar from waste streams, and ocean CDR don’t carry the same carbon debt problem. They remove carbon without first releasing it.
The CDR community has been debating the integrity of biomass carbon credits all week. This preprint adds fuel — pun intended — to the fire.