Greenhouse gas emissions from agriculture

• 1. Introduction

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  Greenhouse gas emissions from agriculture climbed 10% between 2000 and 2022, reaching 16.2 billion tonnes of carbon dioxide equivalent. That is a rise of 1.5 billion tonnes in just over two decades. Agriculture, forestry, and land use together contribute between 13% and 21% of all greenhouse gases released on Earth. When the broader food system is factored in, the share rises to 37% of total global emissions. Projections suggest a further 30-40% increase by 2050, driven by population growth and shifting diets. Two gases sit at the center of the problem. Nitrous oxide and methane together account for more than half of all direct agricultural greenhouse gas emissions. What makes farming such a potent source of planet-warming gases? Which practices carry the heaviest burden? And what would a genuine response require?

• 2. The Ruminant Problem

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  In 2010, enteric fermentation alone accounted for 43% of total greenhouse gas emissions from all agricultural activity in the world. Cows, sheep, and other ruminants digest their food through a microbial process in their stomachs. Their burps are the dominant methane source from land use, land-use change, and forestry. A single cow emits 220 pounds of methane each year. Small ruminants such as sheep and goats contribute approximately 475 million tonnes of carbon dioxide equivalent to global emissions. That constitutes around 6.5% of world agriculture sector emissions. Methane produced by ruminant animals makes up an estimated 15-20% of all methane released globally each year.

  Manure left on pasture, applied to soil, and processed through management systems together account for 7-10% of global agricultural greenhouse gas emissions. Livestock also occupies 70% of all land used for agriculture, equivalent to roughly 30% of the entire land surface of the Earth. Despite that scale, livestock farming demands around 30% of agricultural freshwater while supplying only 18% of the global calorie supply. Animal-derived foods account for 39% of worldwide protein supply, with crops providing the larger share.

  Pigs and poultry differ substantially from cattle and sheep in their climate footprint. Classified as monogastric animals, they have a higher feed-conversion efficiency than ruminants and produce far less methane. Meat from ruminants carries a higher carbon footprint than other meats or vegetarian protein sources. This finding is supported by a global meta-analysis of lifecycle assessment studies. Crops such as corn and alfalfa are cultivated specifically to feed livestock, compounding the land-use impact of animal farming. Calls have grown to phase out subsidies currently offered to livestock farmers as part of a just transition toward lower-emission food production.

• 3. Potency and Persistence

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  Methane is 28 times more capable of trapping heat than carbon dioxide. It breaks down in the atmosphere far more quickly than CO2, but its potency per molecule is substantial. Agricultural processes together account for 54% of human-caused methane emissions and roughly 80% of nitrous oxide emissions. They also produce virtually all of the carbon dioxide tied to land use. Farming-related carbon dioxide, generated by tilling fields, planting crops, and shipping products, amounts to around 11% of global greenhouse gas emissions. The manufacture and use of nitrogen fertilizer alone accounts for around 5% of all global greenhouse gas emissions.

  Nitrous oxide is 300 times more effective at trapping heat per pound than carbon dioxide. It persists in the atmosphere for around 120 years. Fertilizers increase crop yields and accelerate plant growth, but their application drives the release of nitrous oxide into the atmosphere. Since 1980, atmospheric nitrous oxide concentrations have increased by 30%. In the United States, agricultural nitrous oxide accounts for 6% of the country's total greenhouse gas emissions.

  The European Union's emissions trading scheme covers around 40% of EU greenhouse gas emissions, yet the agricultural sector is exempt from its requirements. Agriculture is often not included in government emissions reduction plans more broadly. That absence of direct carbon pricing leaves much of the sector without a financial incentive to cut its emissions.

• 4. Land Use and Rice

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  Rice paddies carry a near-term warming impact equivalent to all the carbon dioxide released by aviation worldwide. Traditional rice cultivation ranks as the second largest agricultural methane source on Earth, behind only livestock. Flooded paddies allow organic matter to decompose without oxygen, producing methane as a byproduct. Land cover has changed substantially since 1750, when human expansion began clearing temperate forests to make room for fields and pastures. That clearing increases the albedo of affected areas, producing effects that can either warm or cool local climates depending on conditions. It also reduces the land's capacity to absorb carbon dioxide, raising atmospheric concentrations of the dominant greenhouse gas. Methods such as slash and burn add directly to these effects, releasing greenhouse gases and particulate matter such as soot into the air. Land clearing can also destroy the soil carbon sponge, a store of accumulated carbon built up over long periods.

  Emissions from agricultural soils are shaped by soil type, local climate, and management practices, according to a 2023 review of the research. Conservation tillage, which reduces the frequency or depth of plowing, can lower emissions while enhancing soil carbon storage. Precision agriculture targets inputs only where and when they are needed, cutting both methane and nitrous oxide output. Biochar, produced from organic waste, can lock additional carbon into agricultural soils. Returning biomass residue from crops to the soil and reducing the area of fallow land also lower carbon dioxide output. Increasing the use of cover crops provides similar benefits.

  Drip irrigation and careful monitoring of soil nutrients help avoid overfertilization, one of the key drivers of nitrous oxide release. Some argue that carbon accounting should factor in the opportunity cost of land used inefficiently. Counting that cost would highlight the full climate value of improving agricultural productivity.

• 5. The Road Forward

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  A 2022 study found that quickly ending animal agriculture could provide half the greenhouse gas reductions needed. That would be enough to meet the Paris Agreement's 2-degree warming target. A 2023 study found that a fully vegan diet reduced individual emissions by 75%. The IPCC's Sixth Assessment Report came out in 2022. It stated that diets high in plant protein and low in meat and dairy are associated with lower greenhouse gas emissions. The same report found that a shift toward higher plant protein with moderate animal-source food intake could lead to substantial decreases in emissions. Additional benefits would include reduced land occupation, lower nutrient losses, health improvements, and reduced mortality from diet-related non-communicable diseases.

  Genetic selection, the introduction of methanotrophic bacteria into the rumen, vaccines, and changes to feed are all under investigation. Each approach aims to reduce methane output from livestock without eliminating animal farming. The seaweed species Asparegopsis armata is being tested as a feed additive with the potential to reduce methane production inside ruminant stomachs. Milk substitutes and meat alternatives are among the options identified for reducing dietary emissions on the demand side.

  Of the Shared Socioeconomic Pathways used by the IPCC, only SSP1 offers a realistic possibility of meeting the 1.5-degree Celsius warming target. That pathway assumes animal-derived food will play a smaller role in global diets than it currently does. Net zero plans in some countries now involve limits on total livestock headcounts. Substantial reductions have been proposed in countries with large animal agriculture sectors, including Ireland. An outright end to meat consumption is not currently considered a realistic global goal.

  The USAID Feed the Future project operates across 20 value chains in 12 countries and focuses on food loss and waste. Its analysis found that addressing losses in dairy systems alone could reduce food loss by 4-10%, with direct consequences for greenhouse gas emissions. Researchers divide food system mitigation into four categories: demand-side changes, ecosystem protections, on-farm mitigation, and supply chain action. Research in New Zealand found that switching toward a healthier, lower-emission diet would cost approximately 1% of the country's agricultural export revenue. That cost is an order of magnitude below the estimated savings to New Zealand's health system from the same dietary shift.