Agriculture’s Greenhouse Gas Emissions and Sinks
U.S. farmers and ranchers have long been at the forefront of climate-smart farming, utilizing scientific solutions, technology and innovations to raise crops or care for livestock. These efforts are designed to protect soil and water, efficiently manage manure, produce clean and renewable energy, capture carbon and improve sustainability.
This analysis provides an update on agriculture’s contribution to U.S. greenhouse gas emissions and sinks using the Environmental Protection Agency’s Inventory of U.S. Greenhouse Gas Emissions and Sinks report. The report identifies agriculture’s and other economic sectors’ contributions to greenhouse gas emissions for 2018 and earlier years.
A deep dive into the data reveals that not only is agriculture a distant fourth in a sector-by-sector comparison of contributions to total U.S. greenhouse gas emissions, but if farmers’ carbon sequestration efforts were recognized, their contributions to GHG emissions would be significantly lower. On the livestock front, U.S. producers’ continuous innovation has lowered their per-unit GHG contributions.
Using two measurement methodologies, EPA provides data on greenhouse gas emissions and sinks, i.e., carbon sinks, for various sectors. The first is the measurement by economic sector and the second is based on methodologies consistent with those recommended in the 2006 Intergovernmental Panel on Climate Change. This article will review agriculture’s contribution in both measurement categories.
Greenhouse Gas Emissions by Economic Sector
EPA’s February 2020 Inventory of U.S. Greenhouse Gas Emissions and Sinks report revealed total U.S. greenhouse gas emissions in 2018 of 6.7 billion metric tons in carbon dioxide equivalents, up 2.9%, or 188 million metric tons, from the prior year's 6.5 billion metric tons. When including land use, land-use changes and forestry carbon sinks of 774 million metric tons, net greenhouse gas emissions totaled 5.9 billion metric tons in carbon dioxide equivalents – up 3.1%, or 179 million metric tons, from the prior year.
The increase in greenhouse gas emissions was primarily due to higher emissions from the industry and residential and commercial sectors of the U.S. economy. Figure 1 highlights the trends in greenhouse gas emissions by economic sector.
Representing approximately 28% of all emissions, transportation is the largest economic sector in greenhouse gas emissions. Transportation sector emissions totaled 1.88 billion metric tons in 2018, up 1.6% from 2017. Following transportation was the energy sector, i.e., electric power, representing nearly 27% percent of all emissions and totaling 1.8 billion metric tons. Electric power emissions were up 1.2% from 2017.
Up 4% from prior-year levels, emissions from the industry sector represented 22% of all emissions and totaled 1.5 billion metric tons. Other greenhouse gas emission sources, including commercial, residential and U.S. territories, totaled 867 million metric tons in 2018 and represented 13% of all emissions. These emissions were up 8% from 2017 primarily due to a 14% increase in residential-based heating and cooling needs during 2018.
Agricultural Greenhouse Gas Emissions
EPA estimates that during 2018, agriculture represented 9.9% of all emissions when measured by economic sector. When measured using the United Nations Framework Convention on Climate Change, an international standard, agriculture’s contribution to greenhouse gas emissions totaled 619 million metric tons and represented 9.3% percent of all emissions. Figure 2 highlights agriculture’s contribution to greenhouse gas emissions by sector measurement for 2018.
Greenhouse gas emissions related to agriculture totaled 659 million metric tons in 2018, up 2.5%, or 16.2 million metric tons, from prior-year levels. Additionally, farmers and ranchers also help remove greenhouse gases through the management and preservation of grasslands, wetlands and forestland, which create carbon sinks that store carbon in the soil.
During 2018, forestland management, land converted to forestry, grasslands and wetland management contributed to a 768-million-metric-ton reduction in greenhouse gas emissions. When including total emissions and removals, total land use, land-use change and forestry represented a net emissions reduction of 774 million metric tons. While not all of these carbon sinks are directly related to the activities of farmers and ranchers, when including these sinks, they more than offset agriculture’s direct contribution to greenhouse gas emissions.
The largest agriculture-related greenhouse-gas-producing source category was agricultural soil management at 338 million metric tons, up 3.3%, or 11 million metric tons from the prior year. Soil management practices, such as the application of synthetic and organic fertilizers, deposition of livestock manure and the growth of nitrogen-fixing plants, represented 55% of total agriculture GHG emissions in 2018.
Following soil management, enteric fermentation in livestock contributed 178 million metric tons, up 1.3%, or 2.2 million metric tons, from 2017 and represented 29% of total emissions. Livestock manure management represented 13% of all agricultural emissions and totaled 81 million metric tons in 2018, up 3.3%, or 2.6 million metric tons. Rice cultivation represented 2% of total emissions and totaled 13.3 million metric tons in 2018.
Importantly, a variety of agricultural practices such as the planting of cover crops, conservation tillage and crop rotation can increase the amount of carbon stored in soils. These sequestration efforts, however, are not assigned to agriculture but to the land-use sector. If these carbon sequestration practices were included, the amount of GHG emissions tied to agriculture would be much lower.
Emissions from Animal Agriculture
Based on IPCC measurements, agricultural emissions during 2018 totaled 619 million metric tons. Of that total, 42% of the emissions – approximately 259 million metric tons in CO2 equivalents -- were related to enteric fermentation or manure management. Enteric fermentation emissions totaled 178 million metric tons, up slightly from prior-year levels.
Beef cattle contributed 128 million metric tons, followed by dairy cattle at 44 million metric tons and swine at 2.8 million metric tons. Other livestock, including horses, sheep, goats, bison and mules, contributed 0.62 million metric tons.
As a percentage of total GHG emissions, enteric fermentation from livestock represented less than 3% -- actually 2.66% -- of all emissions in 2018. When manure management is included, livestock-related emissions represented less than 4% of all emissions.
Importantly, the proportion of livestock-related emissions relative to total emissions declined from 2017’s 2.7%. Since EPA began its series in 1990, livestock-related enteric fermentation emissions have never exceeded 2.71% of all emissions. Figure 3 highlights U.S. livestock emissions from enteric fermentation as a share of total GHG emissions.
While total livestock-related emissions as a percentage of total GHG emissions have remained mostly flat for the past three decades, it is important to factor in livestock producers’ productivity gains when evaluating total GHG emissions. Compared to 1990, U.S. milk production has increased by 71%, beef production has increased by nearly 50% and pork production has increased by 17%, while GHG emissions from animal agriculture have remained mostly flat.
To evaluate how the efficiency gains made in animal agriculture have lowered the environmental footprint, the enteric fermentation emissions per unit of production were measured across beef, pork and dairy. Then, the annual values were indexed to their 1990 levels. Compared to 1990, enteric fermentation emissions per unit of beef production have fallen by nearly 10%, pork-related emissions have fallen by nearly 20% and enteric fermentation emissions per unit of milk production have fallen by 25%. U.S. livestock producers are doing more with less, which has lowered their per-unit GHG contributions, Figure 4.
Crop Productivity Lowers Agriculture’s Environmental Footprint
Productivity gains have had a similarly positive effect on crop production. Due to the adoption of precision agriculture and biotechnology across many crops, fewer acres are needed to produce today’s crops than in 1990.
For example, in 2018 U.S. farmers produced 14.3 billion bushels of corn, with an average yield of 176 bushels per acre, on 81 million harvested acres. Farmers in 1990 would have had to harvest 121 million acres to produce the same 14-billion-bushel crop produced in 2018 – that represents an acreage reduction of 39 million acres, or 33%, from 1990. Similar productivity gains mean we are using 4 million fewer acres to produce cotton, 42 million fewer acres to produce soybeans, 8 million fewer acres to produce wheat and 1 million fewer acres to grow rice. Across only these five crops, the productivity and technological gains made in agriculture allow farmers to use nearly 100 million fewer acres to raise corn, cotton, rice, soybeans and wheat than they would have needed in 1990, Figure 5.
Recently released data from EPA puts agriculture’s contribution to greenhouse gas emissions at 659 million metric tons in 2018 and 619 million metric tons based on IPCC measurement. Either way, agriculture in 2018 represented less than 10% of total U.S. GHG emissions – a distant fourth behind the transportation, electricity generation and industrial sectors.
Moreover, agriculture is part of the climate solution as a variety of agricultural practices, such as the planting of cover crops, conservation tillage and crop rotation, increase the amount of carbon stored in soils. Total carbon sink efforts from forestland management, land converted to forestry, grasslands and wetland management more than offset agriculture’s contribution to total emissions. However, many of agriculture’s carbon sequestration efforts are not directly assigned to the agriculture sector. It is certain that if the carbon sequestration efforts of U.S. farmers and ranchers were assigned to agriculture, our contributions to GHG emissions would be significantly lower.
More productive livestock operations allow ranchers, pork producers and dairy farmers to maintain their total contribution to GHG emissions at less than 3%, while also leading to lower per-unit GHG emissions. Similarly, productivity gains in crop production allow farmers to produce more food, fuel and fiber while using at least 100 million fewer acres than three decades ago.
U.S. farmers and ranchers contribute significantly fewer GHG emissions than their counterparts around the world. Additional EPA data shows agriculture’s global contribution to GHG emissions was 24% in 2010, more than double U.S. farmers’ and ranchers’ contributions to total U.S. emissions in 2018. This significant difference is largely driven by farmers’ enthusiastic adoption of technology. Farmers are the pioneers of sustainability and any policy debate should recognize their contributions, efficiency gains and the considerable impact of their carbon sequestration efforts.
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