Carbon removal might seem like a straightforward concept, but it’s been difficult to pin down a strict and useful definition.
In December 2023, we weighed into this debate with a commentary raising concerns about credits from corn ethanol carbon capture and storage (CCS). We argued that these projects should not be called carbon removal because the ethanol production system as a whole adds CO₂ to the atmosphere rather than taking it out, even with CCS.
Our thinking since then has evolved. In a new commentary, written in collaboration with Zeke Hausfather, we summarize the ongoing debate and suggest that there is no simple definition of carbon removal that reliably sorts projects worthy of support from those that are not. That limitation applies to the definition we put forward in our original commentary. Overly accommodating definitions, as we flagged previously, risk justifying support for projects that don’t warrant it. On the other hand, overly conservative definitions discourage funding for projects that are key to developing the carbon removal capacity we’ll likely need long term. Instead of relying on imperfect lines in the sand, our new commentary recommends re-centering the long-term goals of carbon removal, and asking a set of questions that together can help assess the extent to which a technology or process is likely to support those goals.
Thanks to the many people who contributed to our evolution in thought over the past year and a half, including: Corrine Scown, Grant Faber, Matthew Brander, Matthew Gammans, Maurice Bryson, Robert Hoglund, Rory Jacobson, Sarah Baker, and Sarah Nordhal.