Negative CO2 emissions (also known as Carbon Dioxide Removal, CDR) comprises a suite of methods or techniques to sequester carbon from the atmosphere at scale.

The easiest methods by far are those that leverage photosynthesis to convert CO2 to biomass and then prevent the resulting organic matter from being decomposed back into CO2 through decomposition. All of these methods require that large amounts of productive land be devoted to carbon storage, so the total potential for carbon storage by these methods is limited. Chemical uptake of CO2 by accelerated mineral weathering or ocean alkalinity enhancement are more speculative, but may provide carbon sequestration without substantial land tradeoffs. Finally, direct air capture (DAC) is an extremely energy-intensive and costly process for concentrating atmospheric CO2 into liquid sorbent and then extracting the resulting material for long-term storage, perhaps underground.

All known methods for negative CO2 emissions are substantially more costly and difficult than preventing positive emissions by substituting low-carbon energy for fossil energy in the world economy. Nevertheless, these methods may become needed if policy fails to achieve deep decarbonization fast enough to prevent catastrophic damage.

Scott Denning is Monfort Professor of Atmospheric Science at Colorado State University where he studies pathways of carbon in the climate system. Over 30 years, he’s published well over 100 papers in the peer-reviewed climate literature, served on many national and international advisory boards, and mentored dozens of graduate students. Now on transitional retirement from CSU, he’s delighted to be teaching and speaking more and writing fewer proposals and reports. He’s a lively and entertaining presenter and has a notoriously foul mouth.

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