2.13: On the NAS report on negative emissions

As mentioned above several times, in 2018, the US National Academy of Sciences released a detailed, interesting and important report on negative emissions technologies which can be read in full online.

“Safe” achievable scales <$100

With “current technology and understanding”, they estimate a “safe” achievable scale of at best only ~10 GigaTonnes of CO2 annually around the globe across all currently available technologies, in their Table S.1:

table going over properties of different cdr approaches

Potentials for plant based solutions

Of note, their Box 3.1 is more optimistic on bioengineering-enhanced plant based approaches, with potentially 11 GtCO2/yr achievable just with plant based solutions and “frontier technology”

summary table for forest and agriculture scales
The report also argues for fairly aggressive funding for the ARPA-E ROOTS program, as well as some other research. What are their projected impacts of such innovation? With “frontier technology” they estimate 0.8 GtCO2/year sequestration in the USA for agriculture. Compare this to the ROOTS analysis, which stated “Based on this calculation, average annual (averaged over the initial 30 yr period) soil C accrual rates (assuming 100% adoption of improved phenotypes) ranged up to 280 Tg C per year (1026 Tg CO2eq) for the most optimistic scenario of a doubling of root C inputs and an extreme downward shift in root distributions.” One gigatonne is 1000 teragrams, so these estimates roughly agree. So their “frontier technology” version seems to take into account potential ROOTS-related advances and significant adoption thereof.


The NAS report also projects ~0 safe scaling of industrial direct air capture at this moment (see Table S.1), citing economics (cost) and practical barriers for safe scale-up. I think perhaps they basically just noted that this is expensive at present, and thus could inflict an economic damage and thus not be “safe” in a broad sense.

But this says little about the possibilities in a scenario where a) society considered the need to be more dire, or was richer, and thus could bear a larger economic cost, and/or b) where the technology has advanced further — indeed, they are just using this as a statement of the current state of the art, before going into a whole set of recommendations for new R&D to improve things. Everyone interested in this should read their outline of proposed research at the end of this summary document.

Overall, their Table S.1 pasted above deliberately undershoots — which makes sense given that it has “with current technology and understanding” in the title, and is assembled from a consensus of many expert views — what would be technically feasible with next-gen technology and research, and with realistic but aggressive deployment possibilities. That gives an optimistic picture overall, I think, if the technology development and cost reduction curves are pushed hard enough.