Review of the U.S. Farmers and Ranchers in Action White Paper on Building a Scientific Roadmap to a Carbon-Negative Agricultural System (2024)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

2 Committee Review of a Draft White Paper on Building a Scientific Roadmap to a Carbon-Negative Agricultural System GENERAL ASSESSMENT The overall goal of the white paper is essentially captured in its title: to provide a scientific roadmap for achieving carbon-negative agriculture. This is an important subject with an ambitious premise. A roadmap could be influential in focusing needed support for research and agricultural production practices aimed at reducing this major economic sector’s GHG footprint. The white paper addresses the issue of GHG production from agriculture by placing it into the global context of other GHG-producing sectors of the economy and describing some of the key agricultural sources and sinks for carbon and GHGs generally. The report comprises nine chapters, seven of which consider separate technical areas, plus an introduction and a concluding chapter, each authored by separate groups. The report treats many key issues in GHG reduction and mitigation. The authors have put considerable effort into their document, and they are to be commended for addressing this broad and complex subject. The committee found the white paper to have several shortcomings that are briefly summarized here and discussed in greater detail in later sections of this report. Addressing these points will improve the document’s coherence and strengthen the presentation of the central premise. First, the white paper lacks a defined system boundary to frame the various activities described across its chapters, so it is unclear what activities are or are not part of the analysis, with no firm basis for the accounting of estimated GHG emission reductions or carbon sequestration necessary to achieve the goal of carbon-negative agriculture. In some of the technical chapters, promising opportunities within agriculture are not covered or only receive superficial treatment. For example, biopower and wind energy are barely addressed in the chapter on on-farm energy use and production, so it is hard to know the extent to which their contributions to the goal are included. Ideally, each chapter would include a tally of the estimated net emissions reduction, including sequestration potential associated with a set of described activities and ex- pressed as a percent of the total amount anticipated to be needed for the system to reach the net-negative goal. The analysis should also have a temporal element, so the reader can understand over what period the net emissions reductions might be achieved. Second, in addition to a system boundary, the authors should consider addressing the scope of the analysis of the paper with respect to factors that influence or potentially influence the system, such as ad- vances in plant-based and cultured meat and changes in consumer preferences, and policy. For example, much of what is discussed depends on the decisions of producers and the supply chain, and it would strengthen the paper if its chapters, including the final summary, were transparent and realistic about as- sumptions for adoption and described the technical and social barriers that would have to be overcome for implementation, along with some sense of needed incentives. If the addition of these topics is not feasible, the paper should at least raise them as issues that pose challenges to the emissions reduction goal. It may also be appropriate to identify some aspects to be explicitly out of scope and simply note the limits of the white paper in addressing them. Financial incentives that are likely to influence adopting prac- tices that sequester carbon or reduce GHG emissions is an important topic, but the paper can place the detailed analysis of the monitoring, reporting, and verification challenges of soil carbon markets as out of scope for its analysis. The authors might reference literature as the basis of assumptions about adoption, or 4 

Committee Review of a Draft White Paper on Building a Scientific Roadmap information on carbon markets might be addressed separately in a companion paper. Regardless, a state- ment that acknowledges the scope of the analysis and the limit of the white paper is needed so readers are not left wondering about the purpose of this study. Third, each chapter group appears to have mostly worked in isolation, with no common approach to the analysis or harmonization of the findings among chapters. The white paper has very few instances where one chapter refers to another, so it appears as a collection of individual efforts rather than a coherent whole. The tone, level of technical detail, and nature of the treatment varies significantly by chapter, sometimes presenting a scholarly review and documentation of GHG mitigation issues and sometimes advancing prac- tical recommendations of specific procedures to mitigate net emissions. The articulation of the scientific roadmap or priorities is vague in places, so a revision with a common chapter structure would be beneficial. Fourth, the intended audience is unclear, which has implications for the potential impact. Because the white paper was commissioned by USFRA, a private support organization for agricultural interests, the audience might be assumed to be the broad community of agricultural producers and operators of the related supply chains. Because it was written by a team of scientists, it might be aimed at the scientific and policy design community. The document can have multiple audiences; if so, it should identify them and help all of them understand the significance of the material. The report would be strengthened by an executive summary and chapter summaries designed to communicate to the full scope of those audiences, especially because not all will have the scientific expertise to assimilate some technical information. Finally, the white paper’s emphasis on describing steps toward carbon negative feels at times so overly optimistic that it risks leading many to dismiss it as an unsubstantiated assertion. Even the content of some chapters seems to cast doubt on the overall feasibility of the negative emissions goal by expressing alternate goals, such as carbon “neutral.” Adopting a more moderate statement of the effort might improve credibility and acceptance. Overall, however, this white paper has many important ideas and topics that could be communicated more clearly. A more consistent organization, such as common headings throughout the chapters, descrip- tions of life-cycle analyses that are comparable, and a common set of statistics (double-checked for accu- racy and cross-chapter consistency) for making comparisons would all strengthen the sense of a coherent document. Many key statistics do not agree across chapters, and because parts of the white paper were drafted at different times, the references are often dated and sometimes not comprehensive. We recommend that the authors update references for their chapters, especially information from the latest Intergovernmen- tal Panel on Climate Change (IPCC) report to ensure the information is current and relevant. In the following section of this report, the review committee offers discussion of some of the major issues that, if addressed by the authors, would help develop the white paper into a stronger document. In addition, many chapter-specific comments are provided for consideration in Appendix A. The report could be impactful, but without careful attention to the comments noted by the chapter authors, it is unlikely to achieve this potential. MAJOR ISSUES OF CONCERN Defining the Boundary of the System From the outset, it should be made clearer what is meant by “carbon.” It appears to encompass both soil carbon sequestration and reductions of emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The white paper would benefit greatly from a graphic clearly showing the boundaries of the system addressed regarding carbon or GHGs. It would also greatly improve the document if the authors were to clearly define the system boundaries and address what “carbon negative” means. For instance, does the accounting include such things as a) the production of inputs using fossil fuels, such as fertilizer; b) transporting inputs to the farm; c) transportation from farm to processing; d) initial on- or off-farm pro- cessing (drying, storage); e) production of farm equipment; f) energy production on the farm, such as from wind turbines or solar arrays; and g) impact of fertilizer runoff on algae growth, and downstream GHG emissions? These components must be made clear; without this clarity, it isn’t possible to speak to “carbon 5 

Review of White Paper on a Scientific Roadmap to Carbon-Negative Agriculture negative” or “GHG negative.” The white paper would be improved by labeling the considered carbon or GHG streams quantitatively and showing proper balancing equations, because without a material balance, this type of discussion will remain undefined and dangerously soft (as is, incidentally, acknowledged in Chapter 9, the summary conclusions chapter). Given balancing equations, the meaning of “negative” can be understood. As an example, the committee suggests a hypothetical, quantitative figure that it developed (see Figure 2-1), which shows forestry as outside the boundary of analysis. Although forestry is, at least by some defi- nitions, part of agriculture (EPA, see Figure 2-1), and within the mission area of the U.S. Department of Agriculture (USDA), it is only superficially addressed in a couple of the white paper chapters and not at all in the conclusion. To be clear, the committee is not suggesting that forestry be included, only that a graphic of the system boundaries and a statement in the text could confirm its intentional exclusion. FIGURE 2-1 The boundaries of the system for carbon-negative operation. Figure 2-1 was conceived by the committee simply to illustrate one possible way to display the activ- ities included in the system being analyzed. Many other examples in the literature illustrate not only bound- aries but also drivers, such as socioeconomics and policy.1 Toward a Dynamic Boundary In addition to a system boundary, a boundary defined by time frame is needed and should be recon- ciled with the dynamic nature of sequestration. In particular, the chapter on soil carbon sequestration out- lines the approach to equilibrium and saturation characteristics but otherwise offers no acknowledgment in the introduction, goal statement, and final summary that these contributions will not persist forever. A better treatment of the time dimension of the document’s goal would improve its content. 1 See, for example, https://www.nae.edu/276571/Guest-Editorss-Note-Science-and-Engineering-to-Transform-the- Food-and-Agriculture-System-for-the-Future. 6 

Committee Review of a Draft White Paper on Building a Scientific Roadmap Global Warming Potential (GWP) Although the title refers to carbon, it seems from the contents that global warming or GHGs are the actual issue or target to be addressed, as evidenced by the extensive discussion of nitrous oxide (N2O), which does not enter a strict carbon balance. The GWP2 introduced in Chapter 1 is a mechanism to normal- ize potential impacts of different GHGs using a widely accepted approach for calculating CO2 equivalents (CO2e). However, the basis for using this approach in the context of the white paper’s overall premise is not totally clear, as emissions could be expressed in terms of their global warming potential over 20 years (GWP20) and 100 years (GWP100), reflecting that near-term mitigation of CH4 emissions will have a greater impact on slowing climate change during the next 2 decades than will mitigating CO2 or N2O. Slowing warming during the next 2 decades is crucial to slow positive feedbacks to climate change from natural sources, such as GHG emissions from permafrost and wetlands, so expressing results as GWP20 in addition to GWP100 would help readers understand how effective CH4 mitigation could be between now and 2040 or 2050. This is particularly important for agriculture, because livestock is the largest single source of global anthropogenic CH4 emissions. The authors should clearly state early on what their defini- tion of carbon negativity is and whether their interest is in carbon negativity or global warming in general. Treatment of Implementing Policy and Social Justification for Action The document’s narrative does not deal in much depth with strategies for getting farmers and ranchers to adopt the possibilities discussed across its chapters. Generally, agricultural producers want to make money and control risk and will likely need incentives to adopt many of these possibilities. Such incentives may well involve subsidies through Inflation Reduction Act provisions or USDA programs, institution of a carbon market, publicly developed and disseminated new technologies, and climate-adapted crop varie- ties. The widespread adoption assumptions herein would also require reaching small farmers and rangeland owners. How will that be achieved? Across the chapters, substantial challenges are not mentioned—such as incentive design, measurement and monitoring, additionality, permanence, leakage, uncertainty, trans- actions costs, stimulating adoption, and the nonstationary context introduced by climate change. It might strengthen the white paper’s case if the social cost of carbon were introduced as a measure of social damages that motivate efforts to control net GHG emissions by providing incentives that reward farmers for using some emissions-reducing practices, whether through markets, subsidies, or other incen- tives. A USDA report to Congress describes many of these opportunities (USDA, 2023). Recent estimates of the social cost of carbon indicate that reducing net emissions to the atmosphere can be worth $200 per ton CO2e, which could justify a greater agriculture contribution. As noted, however, defining the scope of the report at its outset and in relevant chapters could help determine which of these topics are worth includ- ing and why. Prospects for Achieving the Goal of Carbon Negative The report authors must keep in sight the stated goal to provide information on ways or strategies to promote carbon-negative (or, more achievably, “low carbon”) agriculture, highlighting successes, chal- lenges, and socioeconomic implications. Many of the chapters are not well organized around the overall theme of how agriculture can address specific emission sources or sequestration possibilities (Chapters 2, 5, and 7, for example). Important topics are missing or only minimally addressed, such as diet shifts, elec- trical biopower from biomass and manure, wind and solar on agricultural lands, rice paddy management, reforestation, and forest management. The white paper also does not address many unknowns that might affect the trajectory of carbon se- questration or emissions reducing practices. How will climate change affect these potential gains and losses 2 See https://www.epa.gov/ghgemissions/understanding-global-warming-potentials#:~:text=The%20Global%20Warm ing%20Potential%20(GWP,carbon%20dioxide%20(CO2). 7 

Review of White Paper on a Scientific Roadmap to Carbon-Negative Agriculture of soil carbon stocks, N2O emissions, and enteric and manure emissions? As noted, the summary calcula- tions of Chapter 9 also have an issue of timing related to accounting for the dynamics of soil carbon ap- proaching a new equilibrium or saturation state. In addition, although the “carbon negative” goal may be defined for agriculture overall, the issue of whether each product or sector should aim to achieve carbon-negative production or the onus is on agricul- ture overall is not explored until the end of the report. For example, the livestock sector is very unlikely to ever be carbon negative, but its emissions could be reduced to cause less burden on cropland management to sequester soil carbon. Furthermore, the impact of reaching carbon-negative production in the U.S. alone is not addressed in a global context. The chapters switch from global to U.S. national statistics, which is sometimes confusing. Although the last chapter makes the case that neutral or negative emissions are plausible for the United States under an ambitious adoption scenario, it does not follow that this is true globally, as indicated by data given in the introductory chapter, even as other researchers suggest that a path forward—one that includes dietary changes—is possible for the global food system (Almaraz et al., 2023). The white paper also cites several publications that give overly rosy assessments of soil carbon sequestration potential. Ra- ther than present the upper limit from those estimates, this report would be improved by taking on a more balanced view. For example, Working Group III of the IPCC AR6 concluded with medium confidence that the mean estimate for the global technical mitigation potential of cropland carbon sequestration is 1.9 (range 0.4–6.8) GtCO2e yr−1, but with only 0.6 (range 0.4–0.9) GtCO2e yr−1 likely to be realized at market prices of USD100 per ton CO2-equivalent (IPCC, 2022). Overall, the committee felt that the material does not live up to the white paper’s title and central premise. Some moderation in purpose and title might be in order. Some scientists in agriculture have made sweeping statements on mitigation potential and had their credibility damaged by findings on cases where the claims were overstated (consider the history of statements on no-till and identification of cases where it does not work). This erodes trust and thus undermines other valuable initiatives in agriculture. An overall more cautious approach would help, with moderation and objectivity about a more guarded bridge to the future. The Research Roadmap The term “roadmap” is used to describe the report’s objective of describing how carbon-negative agriculture could be achieved. However, this is only a roadmap in a very general sense. Roadmaps are more useful when they identify key bottlenecks or impediments to specific paths that have been identified to achieve particular goals and suggest ways to overcome or avoid them. It is unclear whether the “roadmap” the authors sought to create is intended to guide both research and implementation or mostly focuses on the research needed before implementation can move ahead at scale. In addition, a roadmap is not consistently addressed in all the chapters, so a complete path forward does not emerge from the paper. Another stated objective is to provide a prioritized list, but there are not always clear priorities in the individual chapters’ conclusions or for the entire report. A better articulation of the purpose could help guide the conclusions that should be drawn at the end and also allow for readers’ expectations to be in line with what they will receive if they read the entire report. Consistency, Standardization, and Integration Consistency is a challenge for a document that has been created by many authors. For example, the white paper uses numerous and varying units for quantities of GHGs. The presentation would be made more understandable via consistent units. The variation between global values, U.S. values, total emissions, and emission intensity (emissions/ha; emissions/unit of production) make it more challenging to compare among and between chapters. 8 

Committee Review of a Draft White Paper on Building a Scientific Roadmap Inconsistent terminology throughout, including “net zero,” “low carbon,” “negative GHG emissions in agriculture,” and “negative and/or neutral carbon,” needs to be resolved. The white paper would be strengthened by a common structure with similarly labeled sections in each chapter, such as background info (current state), practices with great potential in reducing net emissions, barriers and challenges, research needs, priorities, and conclusions. KEY ISSUES BY CHAPTER Chapter 1 Defining the Need for a Carbon Negative Agriculture The first chapter is important for setting the stage and needs to be restructured for a more coherent flow. It could introduce the system boundaries and scope and then highlight the role of the subsequent chapters in describing the agricultural response. In this way, it can serve as a solid introduction and motivate the audience to read the rest of the white paper. As noted, the GHG emission units used here and those elsewhere in the document (Chapters 1, 3, and 4) must be consistent. This chapter might also incorporate a glossary for the rest of the report, defining terms such as “soil health” (Chapters 1–4), and providing clear explanations for acronyms and scientific names (Chapters 3–4). Chapter 1 could also introduce readers to the elements of a common chapter structure across the white paper. Chapter 2 Challenges and Opportunities for Closing the Crop-Yield Gap This chapter addresses closing yield gaps through various crop breeding and management approaches. Although not explicitly stated, the link to negative GHG emissions presumably is the assumption that any- thing that helps close yield gaps will also increase biomass production of the other plant parts left on or in the soil as crop residue. Increased crop residues would then potentially lead to greater soil carbon seques- tration. However, closing yield gaps may not necessarily always increase inputs of carbon to the soil in proportion to the increased crop yield or reduce net GHG emissions by any other means. Hence, an explicit discussion of how closing yield gaps relates to soil carbon sequestration and net GHG emissions is needed in this chapter, along with the farmer’s need to maintain profitability while avoiding risk. The chapter also addresses how increased inputs of nitrogen (N) and irrigation water could help to close yield gaps, but these increased inputs must be chosen to avoid increased emissions of N2O from increased N fertilizer application and increased energy emissions from withdrawing and delivering water for irrigation. Again, this should be stated more explicitly (i.e., that closing yield gaps could make net- negative GHG emissions more challenging if it requires increased inputs of N and water that would make for ideal conditions for N2O production via nitrification and denitrification). The 4Rs3 are fully reviewed, which is somewhat redundant with Chapter 4 (discussing N2O management). Furthermore, some consider- ation might be given to the impact of temperature increases from global warming on the amount of water required to grow crops (Lobell et al, 2014). Large improvements in water use efficiency will be needed to reach the hoped-for yield increases. Although it focuses on technology, the chapter omits many other technological possibilities that could reduce net GHG emissions. This includes management to address in-field food loss and alternative, lower- emitting varieties that are pest resistant and may reduce pesticide costs, have reduced fertilizer needs, lower water needs, lower tillage needs, and/or exhibit more CO2 uptake possibilities. One could even deal with reflectance of the crop canopy (albedo), increasing livestock and grass productivity, the prospect for shifting to other more productive crop types, and planting crop varieties more stimulated by CO2. Although it would enlarge the scope of this chapter, a broader perspective on technology would be desirable. 3 See https://nutrientstewardship.org/4Rs. 9 

Review of White Paper on a Scientific Roadmap to Carbon-Negative Agriculture Chapter 3 Soil Carbon Sequestration on U.S. Agricultural Lands The estimate of 100–200 million metric tonnes (MMT) of carbon dioxide equivalents (CO2e) dis- cussed in Chapter 3 should be put into perspective by comparing it to the 0.6 gigatonne (Gt) target value indicated in Chapter 1 (an example of the inconsistency of units). The potential soil carbon sequestration estimates should also be put into perspective with total U.S. GHG emissions. Every little bit helps, but the last sentence of the chapter could be misconstrued to mean that the soils could be a large part of the solution to reducing total national emissions. However, at most, they can be only a relatively small part of national emission reductions across all sectors (maybe one-third of the 10 percent contribution of agriculture to total GHG emissions). Integrating animal and crop production systems, including grazing of cover crops, is a central tenet of regenerative agriculture. However, it appears to have major impediments to adoption (see detailed com- ments in Appendix I). Some discussion of the reasons that this attractive idea is not being widely adopted in the United States would be helpful. The chapter could also highlight regional limitations for certain practices and provide specific references or examples for regenerative agricultural practices. This chapter does not address how climate change will likely affect potential gains and losses of soil carbon stocks resulting from adopting best management practices. It seems likely that a warmer, possibly wetter, climate would result in higher rates of soil organic matter decomposition, making the hoped-for soil carbon gains more difficult to achieve. This is speculative, but it would be desirable to make the reader more aware of this source of uncertainty. The chapter would also be strengthened by including information on reducing uncertainty in measuring, monitoring, and modeling soil organic carbon accrual. The chapter might emphasize interdisciplinary approaches in soil carbon management research. The concept of “codevelopment of knowledge with farmers” also would be a valuable addition in the chapter’s discussion and Table 4. Perhaps it is most apt for the row on socioeconomic barriers because it is important to make sure that “outreach” is not presented as a one-way download of knowledge from “experts” to farmers but rather a two-way exchange and codevelopment of knowledge. However, including the concept of the engagement of farmers in all types of research would likely be valuable because many of them have ideas and experience on technical aspects and socioeconomic aspects of innovation. This concept would strengthen the main text and this table. Finally, given the large contribution from pasture and range that is incorporated in the quantitative analysis, it would be helpful to improve presentation of that subject, including practices, expected rates of sequestration, ways of incentivizing producers, and challenges that arise due to the prevalence of low-level management of livestock grazing. Similarly, the issue of dealing with smaller farms on the crops side could be addressed. Chapter 4 Climate Mitigation and Nitrogen Agricultural Opportunities to Abate Nitrous Oxide (N2O) Emissions Chapter 4 would be strengthened by discussions on socioeconomic feasibility, practical challenges, and incentives/barriers for farmers when adopting regenerative agricultural practices. So far, few farmers have reduced N application rates even when using enhanced efficiency fertilizer (EEF) products and nitri- fication inhibitors. It should be emphasized that convincing risk-adverse farmers that they can apply less N is a significant challenge, even if EEFs and inhibitors are shown to be effective. Many apply excess N as a risk management strategy. This brings up the importance of socioeconomic research. This report considers known technologies, but green ammonia (produced using renewable energy as opposed to fossil fuel) may be just around the corner, with large investments already being made by industry for marine shipping fuel. How would it affect fertilizer management, especially if it can be synthesized on the small scale of a farm or farmers’ cooperative? Would there be less fall fertilizer application and more split application or simply result in more overall N application if costs decline and availability increases? 10 

Committee Review of a Draft White Paper on Building a Scientific Roadmap To improve this chapter, the authors could consider moving the GWP explanation to the introductory chapter or glossary, ensure consistency in crop names and scientific names, provide explanations for terms, such as “circular agricultural systems,” and improve clarity and consistency in the use of terms. Chapter 5 Animal Protein Production Challenges and Opportunities Chapter 5 would be strengthened by acknowledging that, although reducing livestock emissions is critically important, it will never be zero or negative. Generally, this chapter is about reducing emissions, thus reducing the burden on row crop agriculture or other lands to sequester enough soil carbon to offset the livestock emissions. Chapter 5 might be improved by including graphics, illustrating, for example, a comparison among animal sectors, which would clarify the overall picture. The pork production discussion mentions the “cra- dle to farmgate” carbon footprint of pork, which would be a good comparative measure for all systems. The chapter covers different animal production sectors, focused primarily on cattle, beef, and dairy, although it does treat pork, poultry, and small ruminants. Some of the messaging is unclear, such as that the treatment of life-cycle analysis is hard to follow in terms of what is included (such as GHG emissions attributable to feeds) because the papers referenced cover feed in different ways and along with other production topics. The uneven treatment in the literature remains a source of confusion in this section. Additionally, the take- away message under grazing management for legumes is confusing, and how to achieve the recommended “balance” of carbon and N for animal nutrition is not clear. Aquatic animal production goes unconsidered. The feeds used in aquaculture are increasingly plant protein based and share many of the issues of other animal protein production systems. Furthermore, the trend toward insect-based feeds, although in early stages now, is not considered. However, it could have a positive impact in terms of low GHG emissions and being able to consume food and feeds that are currently wasted and contribute to methane production. This chapter could be more effective if it were organized around GHG emission by source (feed, enteric, manure) rather than by animal, because, for example, the reader is directed to find manure manage- ment for beef cattle under the dairy section, requiring switching between different animal sections. The chapter also fails to treat the issue of manure management in production systems for all the different animal species. The treatment of animal welfare is uneven across the production sectors and somewhat tangential to the overall goals of the white paper. Although this is an important topic, most of the mentions are about poultry production. Is most of the concern in poultry, or is a more even treatment of this topic needed across animal systems? In addition, where do GHGs come in? Generally, if the GHG impact of changing rearing practices, such as “no antibiotics ever” or “cage-free” production, were discussed, including that material would make more sense. As it is, the connection of animal welfare to GHG mitigation is not addressed. The discussion of avoiding the loss of grazing lands and increasing carbon sequestration in grazing land soils is compelling. Nevertheless, the factors (social, financial) leading to conversion of grazing lands are not outlined. Nor are the challenges of the rather extensive and low levels of management of grazing lands and the implication for increasing sequestration. Chapter 6 Challenges and Opportunities for Energy and Efficient Energy Use Because agriculture plays a vital role as a supplier of alternative energy through liquid fuels, feed- stocks for electricity, and wind and solar on agricultural lands, it would be desirable to expand coverage of these approaches in this chapter. Many potential approaches to improving energy efficiency are omitted. Other issues that could be better covered include fertilizer, fossil-fuel-based chemicals, and irrigation water pumping, which may have energy-reducing solutions there. 11 

Review of White Paper on a Scientific Roadmap to Carbon-Negative Agriculture More clarity is needed on whether energy consumption by the agricultural sector considered in this chapter includes usage by both crop and animal production (i.e., the problem of the definition of the study’s boundaries, discussed earlier). Similarly, what is the definition of a “farm” in this context? Is this only for row cropping systems, horticultural crops, animal production, or mixtures? Finally, little is discussed on energy use in postproduction systems, such as food processing, freezing and packaging, and transport. Chapter 7 The Climate Impact and Mitigation Potential of U.S. Food Loss and Waste The authors should define the scope of the issues covered in this chapter to give readers a better ori- entation to all the dimensions of food loss and waste. For example, in its coverage of food waste, the chapter begs the question of the role of diet manipulations, such as portion sizes in meals at home and restaurants, among other consumption-related issues. Are there ways to incentivize changes in consumer diets to reduce the GHG content involved in production of consumed foods? Because this is at the top of the list for poten- tial emissions reduction (Figure 2 in the chapter), it merits more attention. EPA has also replaced its food waste hierarchy guide with the “wasted food scale,”4 which should be used rather than the inverted pyramid graphic. The authors use an excerpt from another publication, which results in some redundancies and periph- eral topics. A rewrite could improve flow, reduce redundancies, and ensure that all topics imported from the other document are relevant to the present objective. For example, it is not clear how soil health is necessarily linked to reducing post-harvest loss or why the two well-crafted paragraphs on regenerative agriculture are linked to the food waste topic of this chapter. Additional clarity is needed regarding the impediments to directing more food waste to animal feed, how impediments can be overcome “using 21st century technology and practices,” the pros and cons for both growers and retailers to participate in contract programs, how the food hubs that are “already in place” are run (by governments, NGOs, or private sector?), a vision for how food hubs should be supported and managed, and how defining compost products affects their use. The feasibility of moving wastes back to more distant fields also raises issues of transport costs, as uncertain, varying year-to-year waste supplies may compromise the potential of a continuous compost operation. Chapter 7 might be reorganized to address basic mechanisms, such as 1) reducing the amount needed to produce; 2) taking waste back to the farm; 3) moving waste away from landfill, avoiding CH4 but emitting recycled CO2; 4) informing consumers about waste to shift preferences away from high waste; 5) giving producers information on lowered waste; 6) contracting and other arrangements to allow lower on-farm production waste; and 7) moving potential waste into alternate forms of consumption, such as food banks. Examples could be cited under these topics. This would eliminate some redundancies. Chapter 8 Economic and Policy Research Challenges and Opportunities Chapter 8 points out that better-integrated models are needed to understand how to drive forward an understanding of the potential for agriculture to do more but does not provide a conclusion or comprehen- sive presentation of the literature of all the analyses that have addressed the role of agriculture in moving toward net-zero emissions. The chapter lacks sufficient discussion of the social science aspects of farmer decision making that are not entirely or even mostly economic. Farmer age, ideology, training, influence of neighbors and com- munities, off-farm employment, small/hobby farms, and trusted sources of information are crucial factors that would affect incentive design and adoption. It would be desirable to call out research needs on those topics. 4 See https://www.epa.gov/sustainable-management-food/wasted-food-scale. 12 

Committee Review of a Draft White Paper on Building a Scientific Roadmap The chapter has a very incomplete literature review and omits the major efforts to examine the com- petitive economic potential of agricultural mitigation, and many issues noted earlier on various types of incentives, including carbon markets (see specific comments in Appendix A). Another question related to scope is whether the chapter might expand its treatment of current ideas about ecolabeling on the carbon footprint of goods and potential role of the consumer. Chapter 9 Conclusions and Summary of Priority Research Needs Chapter 9 provides a list of research topics, albeit not necessarily prioritized. The much-needed re- search on socioeconomic understanding of farmer decision making should be added to the list of research needs. None of the technologies described in the various chapters will have an impact on GHG emissions if they are not adopted, but we know relatively little about the social drivers of farmer decision making. Some of the adoption assumptions are not very credible and diminish the overall credibility of the report. Assumptions on the extent of adoption on crop land and grazing lands are especially tenuous, given the heterogeneity in farm sizes and management extent and low-input nature of most western grazing agri- culture. The soil carbon assumptions for crops and pasture/range are not very credible. The length of time that soil carbon could continue to increase and be maintained is unrealistic and contradicts the soil carbon se- questration chapter. In addition, the 100 years of retention calls for incentives beyond just carbon uptake. As mentioned, GWP20 is as important a metric as GWP100, and it is more so for impacts during the next 2 decades. It would weight CH4 mitigation (e.g., enteric emissions, manure management, and rice management) as more impactful in that time frame. A more transparent discussion of the challenges to achieving net-zero, let alone net-negative, emis- sions would be appropriate for the conclusion. This chapter must reconcile the use of “carbon-neutral” or “carbon-negative” agriculture (whichever the authors agree upon) and summarize the information from all seven chapters concisely. The consensus of the review panel is that “low carbon” might be a better term. CONCLUSION The challenge of harnessing agriculture as a part of a wider, society wide effort to reduce GHG emis- sions as soon as possible while continuing to provide food, fiber, and other services is daunting. Therefore, we applaud the effort to begin crafting a roadmap of possibilities and needed research support. However, we feel that the document suffers from some major inconsistencies, omissions, and a degree of overambi- tion that, if carefully addressed, would improve it and help it succeed in strengthening agriculture’s response to climate change. Much more effort is needed in this arena, including substantial work to refine a scientific roadmap. We also feel that this effort is a first step toward a vital contribution of the agricultural science community to climate change mitigation and hope it serves as a model for additional efforts. REFERENCES Almaraz, M., B. Z. Houlton, M. Clark, I. Holzer, Y. Zhou, L. Rasmussen, et al. 2023. Model-based scenar- ios for achieving net negative emissions in the food system. PLOS Climate 2(9):e0000181. https://doi.org/10.1371/journal.pclm.0000181. IPCC (Intergovernmental Panel on Climate Change). 2022. Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by P. R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, and J. Malley. Cambridge, UK, and New York, NY, USA: Cambridge University Press. https://doi.org/ 10.1017/9781009157926. 13 

Review of White Paper on a Scientific Roadmap to Carbon-Negative Agriculture Lobell, D. B., M. J. Roberts, W. Schlenker, N. Braun, B. B. Little, R. M. Rejesus, and G. L. Haemmer. 2014. Greater sensitivity to drought accompanies maize yield increase in the Midwest. Science 344(6183):516–519. https://doi.org/10.1126/science.1251423. USDA (U.S. Department of Agriculture). 2023. Report to Congress: A General Assessment of the Role of Agriculture and Forestry in U.S. Carbon Markets. https://www.usda.gov/sites/default/files/documents/ USDA-General-Assessment-of-the-Role-of-Agriculture-and-Forestry-in-US-Carbon-Markets.pdf (accessed 06/01/2024). 14