Agricultural activities not only emit greenhouse gases but can change the amount of carbon stored in soils and biomass, thus effectively releasing or absorbing CO2.

Carbon storage is increased by plant growth, which removes CO₂ from the atmosphere during photosynthesis, the process by which plants convert energy from the sun into energy stored in the chemical bonds of carbohydrates, carbon-based molecules.

As discussed in detail in Chapter IV, scientific studies have identified a number of agricultural practices that could help to slow climate change by reducing greenhouse gas emissions or capturing carbon—or both—while maintaining productivity. For example, in 2016, researchers concluded that the expansion of existing USDA conservation practices could lead to the sequestration of 277 MMT CO₂ eq. annually by 2050.⁶⁹ Capturing this volume of carbon in the soil would cut net agricultural greenhouse gas emissions in half. Similarly, agroforestry (incorporating trees and shrubs into cropland and pastureland) and perennial agriculture (plants that live year-round and do not need annual replanting, thus disturbing the soil less) offer significant climate benefits by locking carbon in the perennial biomass of the plant roots and shoots and stimulating a more biodiverse ecosystem that stores more carbon. According to a 2012 review, the widespread adoption of agroforestry practices in the United States could sequester 530 MMT carbon (or close to 2,000 MMT CO₂ eq.) each year, thereby transforming agricultural land into a carbon sink.⁷⁰

Like cropland, rangeland used for livestock grazing can also sequester carbon.

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remain locked in organic matter.⁷¹ However, managing the location and intensity of grazing, while adjusting its timing to facilitate plant growth, can repair these landscapes⁷² and restore their function as carbon sinks.⁷³

As these examples demonstrate, methods already exist to mitigate agriculture’s net contribution to climate change by reducing greenhouse gas emissions or increasing carbon sequestration. However, policies must recognize that while greenhouse gas emissions are permanent actions, biological sequestration is reversible and limited through the natural process of decomposition. Climatic events, such as droughts or wildfires, or human actions, such as resumed tillage, increased grazing, or deforestation, can quickly destroy biomass and disrupt soils, thereby releasing stored carbon.⁷⁴ In addition, gains in soil carbon slow as soils approach a new equilibrium under improved management practices.⁷⁵ (Additional research is needed to clarify how quickly this occurs, but location, prior soil quality, and land management practices all appear to be important factors.⁷⁶)

While sequestration alone cannot offset ever-increasing greenhouse gas emissions, it remains a necessary strategy for avoiding catastrophic climate change. Current levels of atmospheric carbon are so dangerously high that we cannot choose between reducing emissions on the one hand and sequestering carbon on the other.⁷⁷ We must do both.

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Key Recommendations

• Climate change will affect agriculture and the food system more than almost any other sector of the economy. Climate change induced weather changes already jeopardize agriculture with increased floods, droughts, pests, heat waves, wildfires, and more and will force disruptive dislocations as it shifts which crops are suitable for different regions.

• Agriculture occupies 62% of the contiguous U.S. landmass.

• Global food systems contribute approximately one-third of total greenhouse gas emissions, mostly N₂O from soil management and CH₄ from cattle, dairy, and manure, as well as impacts of land use and soil carbon loss.

• In the United States, meat and dairy production, including emissions relating to production of their feed, grazing, enteric fermentation, and manure, accounts for about 80% of agriculture’s greenhouse gas emissions. Yet, Americans receive only 30% of their calories from animal products.

• The vast majority of animal production greeenhouse gas emissions are produced by the very small number of the largest facilities that house almost all the animals produced. Overall, the largest animal production facilities—fewer than 6% of all facilities—produce 89% of the animals and about 85% of the greenhouse gas emissions of all animal production.

• Unless there are significant changes in the food system, agricultural emissions alone will make it impossible to achieve the climate stabilization goal of 2 degrees Celsius, let alone the safer target of 1.5 degrees Celsius. And if meat consumption continues to grow, climate change will be dramatically accelerated.

• Carbon sequestration should be an essential function of agriculture and be supported by federal agricultural programs and policies.

• Other countries are already investing significant sums into agroforestry research and production, yet the United States has lagged, despite robust research demonstrating its significant potential to sequester carbon while producing ample food.

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• Total agricultural greenhouse gas emissions and agricultural emission rates significantly vary among states due to climate differences and the type and intensity of agriculture within each state; state-based policies will likely also need to differ to best address each state’s agriculture sector.

• We must understand the limitations of current research and data in order to craft effective policies.

• Agricultural emissions are much more difficult to calculate than those in other sectors and far less certain. EPA’s estimates for agricultural greenhouse gas emissions must therefore be understood as simply one point in a wide range of possible figures.

• EPA estimates fail to consider impacts of prior land conversion and the lost opportunity to sequester more carbon or release less greenhouse gases from that land; the lost “carbon opportunity cost” contributes as much to climate change as the last decade of fossil fuel emissions.

• EPA analyses do not include in the “agriculture” sector the greenhouse gas emissions of on-farm energy and electricity, annual land use conversion, or production of agricultural inputs. Nor do they include other components of the food system, such as processing, distribution, preparation, and waste. Considering all these emissions together, the food system is responsible for over a third of all U.S. emissions.

• EPA analyses do not calculate the impact of methane in a way that reflects current policy discussions and the need for shorter-term action, reducing its estimate of agricultural emissions by more than half.

• There is ample evidence that many climate-friendly practices significantly reduce emissions or increase sequestration or do both.

• Methods exist to mitigate agriculture’s net contribution to climate change by reducing greenhouse gas emissions or increasing carbon sequestration. However, policies must recognize that while greenhouse gas emissions are permanent actions, biological sequestration is reversible and limited through the natural process of decomposition.

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1. Noah Diffenbaugh et al., Historical Warming Has Increased U.S. Crop Insurance Losses, 16 ENV’T RES. LETTERS 084025 (2021), https://iopscience.iop.org/article/10.1088/1748-9326/ac1223. The study also found “that observed warming contributed almost half of total losses in the most costly single year (2012).”

2.

3. Danielle E. Medek et al., Estimated Effects of Future Atmospheric CO₂ Concentrations on Protein Intake and the Risk of Protein Deficiency by Country and Region, 125 ENV’T HEALTH PERSP. 087002-1 (2017).

4. Jinlong Dong et al., Effects of Elevated CO₂ on Nutritional Quality of Vegetables: A Review, 9 FRONTIERS PLANT SCI. 1 (2018) (finding that elevated atmospheric carbon dioxide (CO₂) levels decreased magnesium, iron, and zinc levels); Samuel S. Myers, Rising CO₂ Threatens Human Nutrition, 510 NATURE 139 (2014) (reporting that most grains and legumes have lower levels of iron and zinc under elevated levels of atmospheric CO₂).

5. See Nathan Rosenberg & Nevin Cohen, Let Them Eat Kale: The Misplaced Narrative of Food Access, 45 FORDHAM URB. L.J. 1091 (2018) (discussing the root causes of food insecurity and diet-related health disparities).

6. DANIEL P. BIGELOW & ALLISON BORCHERS, U.S. DEPARTMENT OF AGRICULTURE, MAJOR USES OF LAND IN THE UNITED STATES, 2012, at 4 tbl.1 (2017) (EIB-178).

7. Id.

8. See Peter Lehner, Feed More With Less, 34 ENV’T F. 42, 49 (2017).

9. See Global Calculator, Home Page, tool.globalcalculator.org (last visited Oct. 28, 2020). See also Michael A. Clark et al., Global Food System Emissions Could Preclude Achieving the 1.5° and 2°C Climate Change Targets, 370 SCIENCE 705-08 (2020) (noting that the global food system is responsible for about 30% of global greenhouse gas emissions and that “current trends in global food systems would prevent the achievement of the 1.5°C target and, that … [m]eeting the 1.5°C target requires rapid and ambitious changes to food systems as well as to all nonfood sectors”).

10. Francesco Tubiello et al., Greenhouse Gas Emissions from Food Systems: Building the Evidence Base, 16 ENVTL.

11. See id. See also Sinead Leahy et al., Challenges and Prospects for Agricultural Greenhouse Gas Mitigation Pathways Consistent With the Paris Agreement, 4 FRONTIERS SUSTAINABLE FOOD SYSTEMS 69 (2020); Eva Wollenberg et al., Reducing Emissions From Agriculture to Meet the 2C Target, 22 GLOBAL CHANGE BIOLOGY 12 (2016); Stefan Frank et al., Agricultural Non-CO₂ Emission Reduction Potential in the Context of the 1.5C Target, 9 NATURE CLIMATE CHANGE 66 (2019); BRENT KIM ET AL., JOHNS HOPKINS CENTER FOR A LIVABLE FUTURE, THE IMPORTANCE OF REDUCING ANIMAL PRODUCT CONSUMPTION AND WASTED FOOD IN MITIGATING CATASTROPHIC CLIMATE CHANGE (2015); Walter Willett et al., Food in the Anthropocene: the EAT–Lancet Commission on Healthy Diets From Sustainable Food Systems, 393 THE LANCET 447-92 (2019); TOMAS NAUCLe & PER-ANDERS ENKVIST, MCKINSEY & COMPANY, PATHWAYS TO A LOW-CARBON ECONOMY: VERSION 2 OF THE GLOBAL GREENHOUSE GAS ABATEMENT COST CURVE (2009).

12. U.S. EPA, INVENTORY OF U.S. GREENHOUSE GAS EMISSIONS AND SINKS: 1990-2019, at 5-1 (2021), https://www.epa.gov/sites/production/files/2020-02/documents/us-ghg-inventory-2020-main-text. pdf. The 2019 emissions are more than 1% higher than those from just the prior year, 2018.

13. Compare id., with U.S. EPA, GREENHOUSE GAS EMISSIONS FROM A TYPICAL PASSENGER VEHICLE (2018) (a typical passenger vehicle emits 4.6 metric tons of CO₂ annually).

14. See U.S. EPA, Overviewof Greenhouse Gases, https://www.epa.gov/ghgemissions/overview-greenhousegases (last updated Sept. 8, 2020).

15. U.S. EPA, INVENTORY OF U.S. GREENHOUSE GAS EMISSIONS AND SINKS: 1990-2018, Box 5-3 at 5-36 (2020) (EPA 430-R-20-002), https://www.epa.gov/sites/production/files/2020-04/documents/us-ghg-inventory-2020-main-text.pdf). In the methodology used by EPA to calculate nitrous oxide emissions, microorganisms in soil produce nitrous oxide at rates dependent on the availability of nitrogen, land use and management, weather, soil types, and other environmental conditions.

16. See U.S. EPA, supra note 15, at 5-2 tbl.5-1.

17. See id. at 5-25 tbl.5-15.

18. Andy Thorpe, Enteric Fermentation and Ruminant Eructation: The Role (and Control?) of Methane in the Climate Change Debate, 93 CLIMATE CHANGE 407, 411 (2009).

19. See U.S. EPA, supra note 15, at ES-7 tbl.ES-2, 5-2 tbl.5-1.

20. See id. at 5-2 tbl.5-1.

21. See NATIONAL AGRICULTURAL STATISTICS SERVICE, USDA, 2017 CENSUS OF AGRICULTURE, U.S. NATIONAL LEVEL DATA tbl.12 (2019). NASS uses different class sizes than does EPA in its definition of a “concentrated animal feeding operation” under the Clean Water Act. Pursuant to EPA rules, a large concentrated animal feeding operation (CAFO) is one with more than 1,000 animal units. An animal unit is defined as an animal equivalent of 1,000 pounds live weight and equates to 1,000 head of beef cattle, 700 dairy cows, 2,500 swine weighing more than 55 pounds, 125,000 broiler chickens, or 82,000 laying hens or pullets. See 40 C.F.R. §122.23(b)(4).

22. See NATIONAL AGRICULTURAL STATISTICS SERVICE, supra note 21, at tbl.25.

23. See id. at tbl.12.

24. See id.

25. See id.

26. See id.

27. Th sources were responsible for 421.8 MMT CO₂ eq. or 78% of agricultural emissions in 2017. Compare U.S. EPA, supra note 15, at 5-2 tbl.5-1 (showing annual emissions from agriculture by source), with infra note 35 (calculating emissions from agricultural soils devoted to feed crop production or grazing).

28. JUSTIN AHMED ET AL., MCKINSEY & CO., AGRICULTURE AND CLIMATE CHANGE: REDUCING EMISSIONS THROUGH IMPROVED FARMING PRACTICES 5 (2020).

29. See C. Alan Rotz et al., Environmental Footprints of Beef Cattle Production in the United States, 169 AGRIC. SYSTEMS 1 (2019).

30. Matthew N. Hayek & Rachael D. Garrett, Nationwide Shift to Grass-Fed Beef Requires Larger Cattle Population, 13 ENV’T RES. LETTERS 0845005 (2018).

31. See BIGELOW & BORCHERS, supra note 6.

32. There were approximately 310 million acres of harvested cropland in 2007 according to the Census of Agriculture. NATIONAL AGRICULTURAL STATISTICS SERVICE, U.S. DEPARTMENT OF AGRICULTURE, 2007 CENSUS OF AGRICULTURE: U.S. NATIONAL LEVEL DATA 16 tbl.8 (2009). The U.S. Department of Agriculture (USDA) estimates that approximately 165 million of those acres were devoted to feed crops; however, up to 10% of the feed was diverted to biofuels. CYNTHIA NICKERSON ET AL., USDA, MAJOR USES OF LAND IN THE UNITED STATES, 2007, at 20 (2011) (EIB-89). This total does not include soybeans, which USDA considers a “food crop,” despite the fact that soybean meal is typically used as animal feed. TANI LEE ET AL., USDA, MAJOR FACTORS AFFECTING GLOBAL SOYBEAN AND PRODUCTS TRADE PROJECTIONS (2016).

33. Conventionally grown feed crops, such as corn, soybean, and hay, generally result in high N₂O emissions. See EPA, supra note 15, at 5-23.

34. The feed conversion ratio expresses the number of pounds of grain necessary to increase the “live weight” of a head of cattle by one pound. At industrial feedlots, a feed conversion ratio of 6:1 is common. DAN W. SHIKE, BEEF CATTLE FEED EFFICIENCY 3 (2013). About 40% of the live weight of a head of cattle is sold as beef, which means that 15 pounds of grain is necessary to yield one pound of beef. See ROB HOLLAND ET AL., UNIVERSITY OF TENNESSEE INSTITUTE OF AGRICULTURE, How MUCH MEAT TO EXPECT FROM A BEEF CARCASS 9 (2016) (PB-1822).

35. This includes grassland emissions, which account for 73.3 MMT CO₂ eq., as well as 48% of cropland emissions—the approximate percentage of harvested cropland devoted to feed crop production in 2007—which adds an additional 92.7 MMT CO₂ eq. Compare U.S. EPA, supra note 15, at 5-2 tbl.5-1, 5-25 tbl.5-15 (showing annual emissions from agriculture by source), with supra note 32(explaining how the percentage of harvested cropland devoted to feed crop production was calculated). Together, they were responsible for 166 MMT CO₂ eq. or 62% of all emissions from agricultural soils in 2016. This total does not include the approximately 16.5 million acres devoted to the production of biofuel feedstock. See supra note 32.

36. USDA Economic Research Service, Seventy Percent of U.S. Calories Consumedin 2010Were From Plant-Based Foods, https://www.ers.usda.gov/data-products/chart-gallery/gallery/chart-detail/?chartId=81864 (last updated Jan. 6, 2017).

37. Matthew Hayek et al., The Carbon Opportunity Cost of Animal-Sourced Food Production on Land, 4 NATURE SUSTAINABILITY 21 (Jan. 2021) (annualized, U.S. carbon opportunity cost of approximately 264 MMT shared through personal communication with author and supplementary materials).

38. Id.

39. Id.

40. Timothy Searchinger et al., Assessing the Efficiency of Changes in Land Use for Mitigating Climate Change, 564 NATURE 249 (Dec. 13, 2018).

41. Id. at 250.

42. See, e.g., FOOD AND AGRICULTURE CLIMATE ALLIANCE, FOOD AND AGRICULTURE CLIMATE ALLIANCE PRESENTS JOINT POLICY RECOMMENDATIONS (2021), https://agclimatealliance.com/files/2020/11/faca_recommendations.pdf (recommendations of coalition led by American Farm Bureau Federation, Environmental Defense Fund, National Council of Farmer Cooperatives, and National Farmers Union to new administration and Congress including providing tools “to maximize the sequestration of carbon” to “achieve the highest number of appropriate soil health-focused practices on the highest number of acres in order to sequester carbon and reduce other GHGs”).

43. Jonathan Sanderman et al., Soil Carbon Debt of 12,000 Years of Human Land Use, 114 PROC. NAT’L ACAD. SCI. 9575-9580 (Sept. 2017), https://doi.org/10.1073/pnas.1706103114 (modeling soil organic carbon indicates a global soil carbon debt due to agriculture of 133 billion metric tons of carbon, with the rate of loss increasing dramatically in the past 200 years). Note that approximately 440 billion metric tons of carbon have been released by fossil fuel burning since between 1850 and 2018. See Pierre Friedlingstein et al., Global Carbon Budget 2019, 11 EARTH SYST. SCI. DATA 1783-1838 (2019), https://doi.org/10.5194/essd-11-1783-2019.

44. Hayek, supra note 37, at 22, fig.2.

45. U.S. EPA, supra note 15, at 6-109 to 6-110.

46. See id. tbl.2-10.

47. Id. tbl.6-1, at 6-34. EPA uses land use history data from the USDA Natural Resources Conservation Service to determine the acreage of land that has been converted to cropland or has remained as cropland, and then models emissions. Id. at 6-54 to 6-72. Over the past several years, the conversion of forest to cropland has resulted in the largest land use-related annual emissions of CO₂. Id. at 6-34.

48. See, e.g., Claudia Hitaj et al., Greenhouse Gas Emissions in the United States Food System: Current and Healthy Diet Scenarios, 53 ENV’T SCI. TECH. 5493–5503 (2019).

49. See supra notes 9–11. See also Sonja J. Vermeulen et al., Climate Change and Food Systems, 37 ANN. REV. ENV’T RESOURCES 195–222 (2012); PRIYADARSHI R. SHUKLA ET AL., INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE, CLIMATE CHANGE AND LAND: AN IPCC SPECIAL REPORT ON CLIMATE CHANGE, DESERTIFICATION, LAND DEGRADATION, SUSTAINABLE LAND MANAGEMENT, FOOD SECURITY, AND GREENHOUSE GAS FLUXES IN TERRESTRIAL ECOSYSTEMS 476 tbl.5.4 (2019) (indicating 21-37% of anthropogenic emissions from food systems); HENNING STEINFELD ET AL., FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, LIVESTOCK’S LONG SHADOW 113 tbl.3.12 (2006) (indicating ~18% of anthropogenic GHG emissions are attributed to livestock alone); ROBERT GOODLAND AND JEFF ANHANG, WORLDWATCH, LIVESTOCK AND CLIMATE CHANGE (2009) (indicating 51% of anthropogenic GHG emissions are attributed to livestock alone).

50. INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE, CLIMATE CHANGE 2013: THE PHYSICAL SCIENCE BASIS Ch. 8, at 714 tbl.8-7 (2014).

51. N₂O emissions will also be the primary cause of stratospheric ozone destruction this century. A.R. Ravishankara et al., Nitrous Oxide (N₂O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century, 326 SCIENCE 123, 123-25 (2009).

52. Maryam Etminan et al., Radiative Forcing of Carbon Dioxide, Methane, and Nitrous Oxide: A Significant Revision of the Methane Radiative Forcing, 43 GEOPHYSICAL RES. LETTERS 12614 (2016).

53. Jessica McDonald, How Potent Is Methane?, FACTCHECK.ORG, Sept. 24, 2018, https://www.factcheck.org/2018/09/how-potent-is-methane/.

54. INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE, supra note 49.

55. U.S. EPA, supra note 15, at ES-3.

56. INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE, supra note 49.

57. Id. at 720.

58. See, e.g., Robert W. Howarth, A Bridge to Nowhere: Methane Emissions and the Greenhouse Gas Footprint of Natural Gas, 2 ENERGY SCI. & ENGINEERING 47, 53-55 (2014).

59. See N.Y.S. Env’t Conservation L. § 75-0101(2) (“‘Carbon dioxide equivalent’ means the amount of carbon dioxide by mass that would produce the same global warming impact as a given mass of another greenhouse gas over an integrated twenty-year timeframe after emission.”); Robert Howarth, Methane Emissions From Fossil Fuels: Exploring Recent Changesin Greenhouse Gas Reporting Requirements for the State of New York, 17 J. INTEGRATIVE ENV’T SCI. 69 (2020), https://doi.org/10.1080/194381 5X.2020.1789666.

60. Calculated by the authors using a global warming potential of 84 instead of 25 for the CH₄ emission rates in U.S. EPA, supra note 15, at 5-2 tbl.5-1.

61. See U.S. EPA, supra note 15, at 3-37 tbl.3-17.

62. Id. at 1-26 tbl.1-6.

63. Id. at 5-44 tbl.5-20.

64. Id. at 5-8 tbl.5-6.

65. See U.S. EPA, Greenhouse Gas Equivalencies Calculator, https://www.epa.gov/energy/greenhouse-gasequivalencies-calculator (last updated Mar. 2020).

66. U.S. EPA, supra note 15, at 5-16 tbl.5-9.

67. Matthew Hayek & Scot Miller, Underestimates of Methane From Intensively Raised Animals Could Undermine Goals of Sustainable Development, 16 ENV’T RES. LETTERS 063006 (June 2021), https://iopscience.iop.org/article/10.1088/1748-9326/ac02ef.

68. Calculated by the authors using the sum of direct and indirect sources in id. at 5-44 tbl.5-20.

69. Adam Chambers et al., Soil Carbon Sequestration Potential of U.S. Croplands and Grasslands: Implementing the 4 Per Thousand Initiative, 71 J. SOIL & WATER CONSERVATION 68A, 70A (2016). This total represents four times the carbon sequestration of forest soils. See Rattan Lal et al., Achieving Soil Carbon Sequestration in the United States: A Challenge to the Policy Makers, 168 SOIL SCI. 827, 838 (2003) (finding that forest soils could sequester 63 MMT CO₂ eq. annually).

70. Ranjith P. Udawatta & Shibu Jose, Agroforestry Strategies to Sequester Carbon in Temperate North America, 86 AGROFORESTRY SYS. 225, 239 (2012).

71. See John Carter et al., Moderating Livestock Grazing Effects on Plant Productivity, Nitrogen, and Carbon Storage, 17 NAT. RESOURCES & ENV’T ISSUES 191, 191-92 (2011).

72. Sherman Swanson et al., Practical Grazing Management to Maintain or Restore Riparian Functions and Values on Rangelands, 2 J. RANGELAND APPLICATIONS 1, 10-14 (2015).

73. DAVID LEWIS ET AL., UNIVERSITY OF CALIFORNIA COOPERATIVE EXTENSION, CREEK CARBON: MITIGATING GREENHOUSE GAS EMISSIONS THROUGH RIPARIAN REVEGETATION 22 (2015).

74. Uta Stockmann et al., The Knowns, Known Unknowns, and Unknowns of Sequestration of Soil Organic Carbon, 146 AGRIC. ECOSYSTEMS & ENV’T 80, 82 (2012).

75. Catherine Stewart et al., Soil Carbon Saturation: Concept, Evidence, and Evaluation, 86 BIOGEOCHEMISTRY 19, 25-28 (2007); Stockmann et al., supra note 74, at 94-95.

76. Stockmann et al., supra note 74, at 82.

77. For an informal discussion of carbon sequestration’s potential to help address climate, see Marcia DeLonge, Soil Carbon Can’t Fix Climate Change by Itself—But It Needs to Be Part of the Solution, UNION CONCERNED SCIENTISTS, Sept. 26, 2016, http://blog.ucsusa.org/marcia-delonge/soil-carbon-cant-fix-climate-change-by-itself-but-it-needs-to-be-part-of-the-solution.

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