2. U.S. Agricultural Greenhouse Gas Emissions

The U.S. Environmental Protection Agency (EPA) estimates that 2019 emissions from agricultural activities—growing crops and raising livestock and poultry—totaled about 629 million metric tons of carbon dioxide equivalent

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(MMT CO₂ eq.), accounting for more than 10% of total U.S.

These agricultural emissions are at a minimum roughly equivalent to that produced by 136 million automobiles in a typical year.¹³ However, unlike the greenhouse gas emissions of most other sectors of the economy, which consist of CO₂ released from the burning of fossil fuels, agriculture greenhouse gas emissions consist largely of nitrous oxide (N₂O) from soils and manure and methane (CH₄) from livestock and manure (as shown in Figure 3 on page 40). Agriculture also produces CO₂ from fossil fuel combustion (both on farms and off-site for on-farm electricity) and CO₂ from land conversion, neither of which are included in the EPA sector total. Agriculture is responsible for approximately 80% of U.S. N₂O emissions and 40% of U.S. CH₄ emissions—the same as the entire oil and gas sector’s production emissions.¹⁴

The largest source of U.S. agricultural greenhouse gas emissions according to EPA is agricultural soil management. Activities by microorganisms in soil naturally result in emissions of N₂O, while agricultural practices, management, and land use can stimulate and accelerate these emissions by increasing the availability of nitrogen. Agricultural greenhouse gas emissions are dominated by emissions resulting from application of fertilizer as well as emissions associated with the breakdown of soil organic matter.¹⁵ Soil management generates approximately half of all U.S. agricultural emissions and 93% of all U.S.

The next largest source of agricultural emissions is enteric fermentation, which results from the digestive process of ruminants (largely cows and sheep in the United States) (see Figure 4, page 42). Enteric fermentation creates CH₄, which animals subsequently release into the atmosphere through

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belching and exhalation.¹⁸ Enteric fermentation is responsible for 32% of all agricultural emissions and 27% of CH₄ emissions in the United States.¹⁹ (As discussed below, the relative impact of bovine exhalation would be much greater using more appropriate approaches for calculating CH₄ emissions.)

Manure management activities are the third major category of U.S. agricultural emissions, releasing N₂O and CH₄ in quantities that total 13% of total U.S. agricultural emissions.²⁰ The largest animal facilities—those with over 1,000 cattle on feed, 1,000 dairy cows, 2,000 finishing hogs, 100,000 turkeys sold, 300,000 broilers sold, or over 50,000 laying hens —generate the substantial majority of these emissions. Greenhouse gas emissions from enteric fermentation and manure are largely dependent on the number of animals raised in these facilities, which are heavily concentrated in a small proportion of the largest operations: over 50% of dairy cows in the United States are in the 4% of operations that stock 1,000 or more dairy cows.²¹

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More than 90% of hogs in the United States are in the 12% of facilities that stock 2,000 or more hogs,²² and more than three-quarters of all cattle on feed in the United States are in the 5% of facilities that stock 1,000 or more cattle.²³ As shown in Figures 5 and 6 (see page 44), the climate footprint of animal agriculture is directly correlated to this concentration of inventory, with a few large facilities responsible for the majority of greenhouse gas emissions.

Methane emissions released from soils flooded for rice cultivation and the field burning of crop residues make up more than 2% of total U.S.

The vast majority of agricultural emissions are from animal production, particularly beef and dairy. In the United States, meat and dairy production—including emissions related to production of their feed (which is about half of U.S. crop production), grazing, enteric fermentation, and manure— accounts for almost 80% of agriculture’s greenhouse gas emissions.²⁷ If the global cattle population were a country, it would constitute the second largest greenhouse gas emitter after China.²⁸ Both the grazing stage for cows and the feedlot stage for beef, dairy, swine, and poultry production, as practiced now, produce substantial greenhouse gas emissions.²⁹ Because cows produce only one calf at a time, which nurse for months and then must graze until their bodies can take a grain diet in a feedlot, there are about five cows grazing for each of the close to 30 million cows in feedlots.³⁰ This requires vast amounts of land—almost 800 million acres or about 40% of the contiguous United States is devoted to grazing.³¹

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In addition, approximately half of all harvested cropland is devoted to animal feed crop production, adding to animal agriculture’s already capacious footprint.³² This cropland is often cultivated more intensely than cropland growing human food and often emits more nitrous oxide per acre than the production of crops for human consumption.³³ However, only a fraction of those crop calories is delivered to humans because the feed-to-meat ratio is so inefficient. For example, the production of one pound of beef from feedlot

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cattle requires 15 pounds of grain.³⁴ As a result, grazing and feed crop production contribute almost two-thirds of N₂O emissions from agricultural soils.³⁵

Not only does animal agriculture overall have an outsized impact on climate change, but this impact is—under current production methods—particularly influenced by beef, dairy, and to a lesser extent, swine production. This impact is all the more striking given that Americans receive only 30% of their calories from animal products.³⁶