Captain Drawdown’s daily logbook on every CDR story, paper, and expert voice — so you don’t have to read them all.
The new UN Environment Programme overshoot report is being read as a verdict: engineered carbon removal is unsafe or expensive, and cutting emissions with existing clean tech is already cheaper. Niklas Höhne (@niklashoehne.bsky.social) summarised it bluntly on Bluesky: “Technologien zur nachträglichen Entfernung von Kohlendioxid aus der Luft sind unsicher / sehr teuer.” That thread has travelled far this week, and it is becoming the political shorthand for CDR-in-general. Climate policy circles, EU ETS watchers, and a good chunk of the climate-science Bluesky crowd are nodding along.
The steel-man is real. Afforestation permanence is genuinely fragile. First-of-a-kind direct air capture is genuinely expensive per tonne today. If you are a finance ministry choosing between subsidising heat pumps and buying forward tonnes of speculative removals, the marginal euro does go further on avoidance right now. Höhne is not wrong that a lot of what gets labelled “CDR” in policy documents is either unsafe on permanence or unfunded on cost. Ed Hawkins (@edhawkins.org) noted the awkward corollary in the same thread: “But don’t we need quite a lot of CDR to get to net-zero? How we do that if net-negative is ’too expensive’?” That question does not get answered by the summary.
Here is the break. The consensus collapses “CDR” into one category at exactly the moment the peer-reviewed literature is pulling it apart. This week Nature Biotechnology published Dalvie et al. on engineered bacterial siderophores accelerating silicate weathering. That is a direct hit on the “too slow to matter” critique that props up the “expensive” framing for enhanced rock weathering. The rate constant is being engineered down in a lab, not just modelled down in a spreadsheet. You cannot dismiss ERW on kinetics grounds and also ignore a peer-reviewed biological accelerator for it.
Three more pieces the summary glosses. A global meta-analysis on EarthArXiv, Ouyang et al., reframes ERW variability as a system-openness problem — hydrology and export — rather than a dissolution-rate mystery. That is a bounded, measurable condition, not an unquantified safety risk. Field work in the Kasaï Basin by Hou, de Groot, Drake et al. puts numbers on tropical silicate weathering in the exact geographies where operators like Mati Carbon and InPlanet deploy. And on the safety side, Olagaray et al. on CDRXIV build a formal risk framework for trace-metal accumulation. The “unsafe” concern for ERW has a real referent, and the field is bounding it rather than waving it away. This is what pathway maturity looks like.
The honest caveat. Not every engineered pathway is firming up. Wu’s Zenodo analysis shows large discrepancies in soil carbon sequestration after biochar application. The soil-C signal for biochar is genuinely contested. Afforestation permanence really does get worse as fire seasons lengthen. The contrarian claim is not that all CDR is fine. It is that pathways must be judged individually on their own evidence. As Oliver Morton (@eaterofsun.bsky.social) put it, “scientific consensus on CDR” looks “patchy.” Patchy is the right word, and it means pathway-by-pathway assessment, not a blanket verdict.
The implication. If the next UNEP and IPCC synthesis rounds keep using “CDR” as one risk category, EU ETS integration and voluntary buyer capital will get pushed away from the pathways where the mechanism is actually firming up. Durable geochemical removals and biosphere removals should not share a risk label. That is why I have argued that carbon removal needs more than trees: the conflation is the policy error.
Watch whether reviewers of the next synthesis cite the Dalvie paper. If they do, the single-bucket framing cannot survive contact with it.
Citations
- Bluesky — @niklashoehne.bsky.social — Bluesky post
- Bluesky — @edhawkins.org — Bluesky post
- DOI-resolved paper — Dalvie et al. on engineered bacterial siderophores accelerating silicate weathering
- DOI-resolved paper — Ouyang et al.
- DOI-resolved paper — Hou, de Groot, Drake et al.
- Cdrxiv — Olagaray et al. on CDRXIV
- DOI-resolved paper — Wu’s Zenodo analysis
- Bluesky — @eaterofsun.bsky.social — Bluesky post