Greenhouse gas emissions from agriculture

• 1. Global Emissions Overview

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  One quarter of the world's greenhouse gas emissions result from food and agriculture, according to data collected in 2019. The agriculture, forestry, and land use sectors contribute between 13% and 21% of global greenhouse gas emissions. Direct greenhouse gas emissions include those from rice and livestock farming. Indirect emissions from the conversion of non-agricultural land such as forests into agricultural land are also very important. Total emissions from agrifood systems in 2022 amounted to 16.2 billion tonnes of carbon dioxide equivalent. This figure represents an increase of 10%, or 1.5 Gt CO2eq compared with 2000. In 2020, it was estimated that the food system as a whole contributed 37% of total greenhouse gas emissions. That figure was on course to increase by 30, 40% by 2050 due to population growth and dietary change. Between 2010 and 2019, agriculture, forestry and land use contributed between 13% and 21% to global greenhouse gas emissions. Nitrous oxide and methane make up over half of total greenhouse gas emissions from agriculture.

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• 2. Livestock And Methane

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  Farm animals' digestive systems can be put into two categories: monogastric and ruminant. Ruminant cattle for beef and dairy rank high in greenhouse gas emissions. A single cow will emit 220 pounds of methane per year. While the residence time of methane is much shorter than that of carbon dioxide, it is 28 times more capable of trapping heat. Livestock are responsible for 14.5% of total anthropogenic greenhouse gas emissions. Enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world in 2010. The meat from ruminants has a higher carbon equivalent footprint than other meats or vegetarian sources of protein based on a global meta-analysis of lifecycle assessment studies. Small ruminants such as sheep and goats contribute approximately 475 million tons of carbon dioxide equivalent to GHG emissions. This constitutes around 6.5% of world agriculture sector emissions. Methane production by animals, principally ruminants, makes up an estimated 15-20% of global production of methane. Worldwide, livestock production occupies 70% of all land used for agriculture or 30% of the land surface of the Earth.

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• 3. Land Use And Deforestation

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  Agriculture contributes to greenhouse gas increases through land use in four main ways including CO2 releases linked to deforestation. Land cover has changed majorly since 1750, as humans have deforested temperate regions. When forests and woodlands are cleared to make room for fields and pastures, the albedo of the affected area increases. This can result in either warming or cooling effects depending on local conditions. Substantial land-use change contributions to emissions have been made by Latin America, Southeast Asia, Africa, and Pacific Islands. Land-clearing methods such as slash and burn compound these effects, as the burning of biomatter directly releases greenhouse gases and particulate matter such as soot into the air. Land clearing can destroy the soil carbon sponge. Together, agricultural processes comprise roughly 80% of nitrous oxide emissions and virtually all carbon dioxide emissions tied to land use. The IPCC Sixth Assessment Report in 2022 stated that diets high in plant protein and low in meat and dairy are associated with lower GHG emissions.

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• 4. Fertilizer And Nitrous Oxide

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  Nitrous oxide emission comes from the increased use of synthetic and organic fertilizers. Fertilizers increase crop yield production and allow the crops to grow at a faster rate. Agricultural emissions of nitrous oxide make up 6% of the United States' greenhouse gas emissions. They have increased in concentration by 30% since 1980. While 6% may appear to be a small contribution, nitrous oxide is 300 times more effective at trapping heat per pound than carbon dioxide. It has a residence time of around 120 years. Different management practices such as conserving water through drip irrigation, monitoring soil nutrients to avoid overfertilization, and using cover crops in place of fertilizer application may help in reducing nitrous oxide emissions. The manufacture and use of nitrogen fertilizer contributes around 5% of all global greenhouse gas emissions. A 2023 review emphasizes that emissions from agricultural soils are shaped by factors such as soil type, climate, and management practices.

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• 5. Rice Cultivation Methods

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  Traditional rice cultivation is the second biggest agricultural methane source after livestock. Its near-term warming impact is equivalent to the carbon dioxide emissions from all aviation. Government involvement in agricultural policy is limited due to the high demand for agricultural products like corn, wheat, and milk. By only focusing on dairy systems of 20 value chains in 12 countries, food loss and waste could be reduced by 4-10%. These numbers are impactful and would mitigate greenhouse gas emissions while still feeding the population. Research work by the International Center for Tropical Agriculture measures the greenhouse gas emissions of rice production. Methane (CHa) emissions are measured in tonnes of carbon dioxide-equivalents. Global estimates show that agriculture-related emissions of carbon dioxide account for around 11% of global greenhouse gas emissions. Farm practices such as reducing tillage, decreasing empty land, returning biomass residue of crops to the soil, and increasing the use of cover crops can reduce carbon emissions.

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• 6. Dietary Shifts And Demand

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  A 2023 study found that a vegan diet reduced emissions by 75%. Changes to a diet less reliant on animal products such as plant-based diets are also effective. This could include milk substitutes and meat alternatives. According to a 2022 study quickly stopping animal agriculture would provide half the GHG emission reduction needed to meet the Paris Agreement goal of limiting global warming to 2 °C. There are calls to phase out livestock subsidies as part of a just transition. Research in New Zealand estimated that switching agricultural production towards a healthier diet while reducing greenhouse gas emissions would cost approximately 1% of the agricultural sector's export revenue. That is an order of magnitude less than the estimated health system savings from a healthier diet. The IPCC Sixth Assessment Report in 2022 stated that where appropriate, a shift to diets with a higher share of plant protein, moderate intake of animal-source foods and reduced intake of saturated fats could lead to substantial decreases in GHG emissions.

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• 7. Mitigation Technologies

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  Several methods are also under investigation to reduce the greenhouse gas emissions from livestock farming. These include genetic selection, introduction of methanotrophic bacteria into the rumen, vaccines, feeds, diet modification and grazing management. Research continues on the use of various seaweed species, in particular Asparegopsis armata, as a food additive that helps reduce methane production in ruminants. Mitigation measures in the food system can be divided into four categories including demand-side changes, ecosystem protections, mitigation on farms, and mitigation in supply chains. A 2023 review highlights several mitigation strategies, including conservation tillage, precision agriculture, improved water use, and the application of biochar. These strategies can reduce emissions and enhance soil carbon storage. Farm practices such as reducing tillage, decreasing empty land, returning biomass residue of crops to the soil, and increasing the use of cover crops can reduce carbon emissions.

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