Dec 15 2021

Additions to our CDR database

Freya Chay 
Freya Chay

Since early 2020, we have been building a public database analyzing carbon dioxide removal (CDR) proposals. We’re now updating the database to include an analysis of 11 new proposals submitted in response to Stripe’s Fall 2021 carbon removal procurement. You can easily find these new entries with the search term “Stripe Fall 2021”.

This is our fourth time reviewing CDR proposals, and we applied the same analytical framework as in previous rounds. For more details, see our methods and read about our takeaways from analyzing the Stripe 2020, Microsoft 2021, and Stripe Spring 2021 carbon removal purchases.

Alongside highlighting the database update, we wanted to share three brief observations about what we saw in this round:

01 — Stages of maturity

Across the board, we’re seeing proposals from very early-stage projects. Several of these projects proposed novel approaches with open research questions. As we’ve noted previously, our evaluation framework was designed around projects with existing capacity to perform CDR, whereas many early-stage efforts are still being tested in labs. As such, our framework does not necessarily help identify if an early-stage project is poised to successfully execute on their research or deployment plans. Additionally, our approach to validation does not clearly distinguish whether we cannot validate project claims because of a legitimate concern or because there is simply not yet enough science or data on a novel approach. For each project, please read the notes and comments for more context on validation decisions.

02 — Diversification of focus

This round of proposals features multiple projects solving just one component of a carbon removal system: for example, capture-only or storage-only projects. As the CDR ecosystem evolves, we expect this pattern to continue, with projects specializing in different parts of full carbon removal pathways. If private procurement of carbon removal tons continues to be an important source of support, it will be important to ensure tons are not double-counted and that all components of full removal pathways are sufficiently supported.

To be honest, we’ve found it challenging to treat capture-only and storage-only solutions fairly within our current evaluation framework. Since we designed the framework around the procurement of carbon removal tons, we do not validate a proposal’s permanence claim unless it is substantiated with a clear storage plan and specified partners. As a result, capture-only projects often do not receive a checkmark for permanence. However, the lack of a full permanence story is not a concern for capture-only projects if the focus is supporting specialized parts of an ecosystem that can be combined into full carbon removal pathways. We’re looking forward to a significant redesign in the new year to capture these categorical differences.

03 — Interest in oceans continues

While building the CDR database, we’ve observed growing interest in ocean-based carbon removal. Three of the eleven proposals reviewed in this round interact directly with the ocean, including the first alkalinity enhancement proposals we’ve seen. As emphasized by the recently released National Academy of Sciences report on ocean-based CDR, we lack fundamental knowledge around many ocean-based CDR mechanisms, and there is not yet a clear path to verification of removed carbon — if it’s even possible. Additionally, because many of these approaches involve shifting chemical equilibria rather than removing and storing particular molecules of carbon, they also require a new way of thinking about volume and permanence. Substantially more research and pilot-scale deployments will be needed to validate these approaches, and we think care should be taken with speculative procurements.

As always, we welcome questions and feedback. If you have found value in the CDR database, let us know! As we figure out where to take this work next, it’s helpful to hear what you have found useful and what you think is missing. Reach out at or on Twitter. Finally, thanks to Sadie Frank, Cindy Chiao, and Jeremy Freeman, who all helped out with this round of evaluations.

Questions? Interested in collaborating on these problems?
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