The cheapest way to hit 1.5°C carbon removal targets involves no direct air capture at all. That’s the central finding from researchers at Imperial College London, who modeled optimal CDR (carbon dioxide removal) deployment pathways and found that under full international cooperation, the least-cost portfolio is 74% BECCS (bioenergy with carbon capture and storage) and 26% AR (afforestation and reforestation), with DACCS (direct air carbon capture and storage) completely absent from the mix.

Why it matters

This paper, authored by Solene Chiquier, Mathilde Fajardy, and Niall Mac Dowell, puts hard numbers behind something the CDR community has debated mostly in qualitative terms: what happens to costs and technology choices when countries cooperate versus when they don’t? The answer is stark. Without cooperation, costs rise substantially, the likelihood of actually meeting Paris Agreement CDR targets drops, and DACCS becomes a necessary part of the portfolio, not because it’s preferred, but because countries can’t access the cheaper bio-based options available elsewhere. For anyone building a business case around a specific CDR technology, the geopolitical assumptions baked into your model matter enormously.

The details

The researchers modeled three CDR approaches: AR (planting trees to absorb CO2), BECCS (growing biomass, burning it for energy, and capturing the resulting CO2 for underground storage), and DACCS (using chemical processes to pull CO2 directly from ambient air, then storing it). They examined how these technologies would need to be deployed across regions and over time to meet the CDR volumes implied by 1.5°C-compatible scenarios from the Paris Agreement.

Under the cooperation scenario, countries can trade negative emissions. A nation with abundant biomass resources and geological storage capacity can remove more CO2 than its “fair share” and sell the surplus to countries with fewer natural advantages. This lets the global system lean heavily on BECCS and AR, which are cheaper per ton but geographically constrained. The result: a pathway dominated by bioenergy and forests, with costs minimized by matching CDR activity to wherever the bio-geophysical resources and socio-economic conditions are most favorable.

The non-cooperation scenario flips this. Each country must meet its own CDR obligations using its own resources. Some nations simply don’t have the land, biomass, or storage geology to rely on BECCS and AR alone. They’re forced into DACCS, which is more expensive but can technically be deployed almost anywhere with an energy source and CO2 storage. The paper finds this makes the overall pathway “significantly more challenging and costly.”

One particularly interesting finding: even under cooperation, the most cost-efficient spatial distribution of CDR activity looks nothing like a “fair” allocation based on historical emissions or development status. The cheapest tons of removal cluster in regions with the best resources, not necessarily in the countries that bear the most responsibility for climate change. This creates an obvious equity problem, which the authors address head-on.

An international market for negative emissions

Chiquier and colleagues propose that international cooperation policy instruments, specifically a market for trading negative emissions, could solve both the cost and fairness problems simultaneously. Countries with high CDR obligations but limited domestic potential could pay countries with surplus potential to remove CO2 on their behalf. The host countries earn revenue; the buying countries meet their targets at lower cost than going it alone. In theory, everyone wins.

This is essentially the CDR equivalent of carbon offset markets, but for removals rather than avoided emissions. The researchers argue this mechanism can “incentivise participating nations to meet their share of the Paris Agreement’s CDR objectives, whilst making up for the uneven distribution of CDR potentials across the world.”

Implications

If you’re a DACCS developer, this paper isn’t exactly cheerful reading. It suggests your technology is the fallback option when cooperation fails, not the first choice when things go right. That said, the current geopolitical trajectory doesn’t exactly scream “seamless international cooperation,” which may ironically be the strongest argument for investing in DACCS anyway. The world we’re likely to get, rather than the optimal one, probably needs it.

For BECCS and AR proponents, the paper reinforces that these approaches have a massive cost advantage when deployed in the right locations. But that advantage depends entirely on political frameworks that don’t yet exist. Without a functioning international negative emissions market, the theoretical cheapness of BECCS in, say, Brazil or Southeast Asia doesn’t help a European country struggling to meet its CDR targets.

The paper’s most urgent message is about timing. The authors stress that international cooperation needs to happen “as soon as possible” because delay narrows the set of feasible CDR pathways and pushes costs onto future generations. Every year without cooperation locks in more expensive outcomes.

Caveats

This is a modeling study, and models are only as good as their assumptions. The cost estimates for DACCS have been falling faster than many projections anticipated, and continued learning-by-doing could narrow the gap with BECCS. The paper also treats BECCS sustainability constraints (land use, water, biodiversity impacts) as parameters rather than hard political limits, but in practice, scaling BECCS to 74% of global CDR would face enormous pushback on food security and land rights grounds.

The study was published as a preprint on arXiv in April 2022, so it doesn’t capture the most recent cost data or policy developments like the U.S. Inflation Reduction Act’s 45Q tax credits, which have significantly changed the economics of DACCS in at least one major market. Whether the “no DACCS in the optimal mix” conclusion holds under updated cost curves is an open question worth revisiting.

Source: arXiv