Reviewer’s report 1
Richard Roberts, New England Biolabs (Nominated by Itai Yanai)
This is a timely article that deals with an aspect of climate change that is rarely discussed in a realistic sense, namely carbon capture by bio-engineering plants. In general, previous discussions have focused on the relative impractical nature of employing carbon-capture technologies on a scale sufficiently large to have any significant impact on the amounts of CO2 and methane in the atmosphere. Using back-of-the-envelope calculations DeLisi attempts to show that biological carbon capture could be a practical solution to mitigating CO2 build-up. I am not equipped to deal fully with the math, which should be left to someone more familiar with the practical aspects of plant metabolism. However, the important take-home message from my perspective is that this is an area worth a much fuller exploration. Trees are probably not the ideal example as most of the trees in the world are in forests that could not easily be manipulated or are sufficiently slow growing that it would take decades for them to reach a point where thy might have a significant impact. However, agricultural crops grown for food production might be a better short-term target. First, many are already understood genetically sufficiently well that further modification might be relatively straightforward. They are grown in vast amounts and while converting CO2 to carbonate may not be the ideal way of storing the captured carbon other final products such as carbohydrates might be feasible. Second, they are probably a better choice that most trees because much research would likely be needed to produce trees with the desired properties. Time would be a big issue as typically tree geneticists start their work but have retired and relied on first- or second-generation students to explore the results of their genetic studies. With highly polyploid chromosomes manipulating their genomes can be very tricky. Nevertheless, despite the criticisms above, this is a very useful article that with a small amount of rewriting to mention the practical details of tree biology and introducing the idea that other species some of which might be food plants might offer more practical advantages, might have some impact. In light of the current situation as many ideas as possible need to be aired and tested. We have precious little time left to try and resolve the crises that will arise if climate change continues unabated. The last paragraph is particularly timely. A couple of small points: 1. Figure 1. This is a nice figure, but the numbers are a little difficult to read. 2. P3, line 18. Should read “a net difference of” 3. Figure 2. The colors are a little difficult to distinguish. Perhaps, two of the lines could be dotted for clarity.
Author’s response: Dr. Roberts makes good points, and I’m grateful to him for starting the exchange of ideas. The fact that many agricultural plants are much better understood than trees, and would offer a quicker start is especially important given the urgency of the problem. This point, the importance of a quick start, is reinforced by Fig. 2, which illustrates the dramatic effect of a 20-year delay in implementing a CDR strategy. I chose trees only because they are the single largest CO2 absorbers. With respect to policy, the choice of other plants in the near term is, as Dr. Roberts indicates, crucial and remarks bearing on these issues have been added. More generally, with respect to choices, what’s needed now is a careful vetting by the community of the various technical strategies including the state of the underlying science, plausible timelines and tradeoffs between different approaches, costs, environmental impact, efficacy and governance. This is something that we’re beginning to see for other CDR strategies (see comments by Dr. Patrinos) and will, I expect, soon be starting for synthetic biology.
Reviewer’s report 2
Aristides Patrinos, Chief Scientist, the Novim Group (Nominated by Itai Yanai).
I applaud the message conveyed by the author in this paper. Despite three decades of intensive research, several in depth international assessments of impacts, and a series of conventions and treaties, action on reducing the emission of greenhouse gases in the atmosphere has been at best lackluster.
As the author emphasizes, there is a movement among the serious-minded to focus attention and eventually significant R&D resources to ways of removing carbon from the atmosphere and safely sequester it for long periods of time. The National Academy of Sciences (NAS) has recently released a report: Negative Emissions Technologies and Reliable Sequestration: A Research Agenda (2019). Several organizations are currently converting the NAS recommendations into action plans and I am currently involved in one such effort.
Although biotechnology is included in the range of approaches to capture carbon from the atmosphere and safely sequester it, there, is in my opinion, insufficient emphasis so far on utilizing the most “cutting-edge” tool that the author of this paper has highlighted, systems and synthetic biology. As he has emphasized, it may very well be the most revolutionary game-changer in terms of efficacy and cost. However, I also agree with the author that such a game-changer will also require a comprehensive effort addressing the ecological effects of this biotechnology as well as its ethical, legal, and societal implications.
A few additional comments on this paper:
The delays in adopting renewable technologies has been the availability and relatively low cost of natural gas rather than coal. Moreover, another wild card may be nuclear energy. Facing a possible demise in the US, it nevertheless is proliferating in several parts of the world and may end up with a significant role in mitigating climate change.
On the policy front, the most important instrument for stabilizing greenhouse gas concentrations in the atmosphere is placing a price on carbon, either through a tax or via the purchase of permits to emit it.
Author’s response: Dr. Patrinos correctly identifies natural gas as a primary competitor of renewable technologies, especially in the United States and Russia. I also agree that, as far as the world in total is concerned, nuclear energy is not dead as an important energy source -- although I hesitated to mention it for fear of taking the focus off the main thrust of this article.
Figure 2 illustrates the importance of implementing an effective emission control strategy, but I avoided discussing any specific economic approaches. Dr. Patrinos correctly calls attention, as I now have in the revision, to the importance of a carbon tax, the economics of which has been analyzed in great detail by William Nordhaus, recipient of the 2018 Nobel Prize in economics.
Reviewer’s report 3
Eugene Koonin, NCBI, NLM, NIH (Nominated by Itai Yanai).
In this Opinion article, Charles DeLisi propose the use of engineered plants, with part of the CO (2) that is normally emitted through respiration redirected to the formation of stable carbonates, for climate mitigation by removing CO (2) from the atmosphere. Rough estimates are presented demonstrating a remarkable efficiency of the proposed approach. More general, the article advocates serious consideration of Systems and Synthetic Biology as a source of climate mitigation strategies.
I found the article to be excellent, succinct, original and clear. My only, and certainly, optional suggestion would be to move the calculations of the efficacy of the proposed strategy of CO (2) removal from a footnote to the main text and explain the assumptions behind these calculations in somewhat greater detail.
Author’s response: I appreciate Dr. Koonin’s remarks. The technical details are in a footnote so as not to disrupt the flow of the narrative. I have, however, expanded the explanation, and trust that it is now clear.