One quarter of the world's greenhouse gas emissions result from food and agriculture (data from 2019).[1]
Greenhouse gas emissions from agriculture are large: the agriculture, forestry and land use sectors contribute between 13% and 21% of globalgreenhouse gas emissions.[2]Direct greenhouse gas emissions include those fromrice andlivestock farming.[3]Indirect emissions from the conversion of non-agricultural land such asforests into agricultural land are also very important.[4][5] With regards to direct emissions,nitrous oxide andmethane makeup over half of total greenhouse gas emissions from agriculture.[6] A 2023 review emphasizes that emissions from agricultural soils are shaped by factors such as soil type, climate, and management practices. It also highlights several mitigation strategies, including conservation tillage, precision agriculture, improved water use, and the application of biochar, that can reduce emissions and enhance soil carbon storage.[7]
Farm animals' digestive systems can be put into two categories:monogastric andruminant. Ruminant cattle for beef and dairy rank high in greenhouse gas emissions. In comparison, monogastric, or pigs and poultry-related foods, are lower. The consumption of the monogastric types may yield less emissions. Monogastric animals have a higher feed-conversion efficiency and also do not produce as much methane.[10] Non-ruminant livestock, such as poultry, emit much less greenhouse gas.[11]
There are many strategies to reduce greenhouse gas emissions from agriculture (this is one of the goals ofclimate-smart agriculture). Mitigation measures in the food system can be divided into four categories. These are demand-side changes, ecosystem protections, mitigation on farms, and mitigation insupply chains. On the demand side, limitingfood waste is an effective way to reduce food emissions. Changes to a diet less reliant on animal products such asplant-based diets are also effective.[12]: XXV This could includemilk substitutes andmeat alternatives. Several methods are also under investigation to reduce the greenhouse gas emissions from livestock farming. These include genetic selection,[13][14] introduction ofmethanotrophic bacteria into the rumen,[15][16] vaccines, feeds,[17] diet modification and grazing management.[18][19][20]
World farm-gate greenhouse gas emissions by activity
Total emissions from agrifood systems in 2022 amounted to 16.2 billion tonnes ofcarbon dioxide equivalent (Gt CO2eq) of GHG released into the atmosphere, an increase of 10%, or 1.5 Gt CO2eq compared with 2000.[21]
In 2020, it was estimated that thefood system as a whole contributed 37% of total greenhouse gas emissions and that this figure was on course to increase by 30–40% by 2050 due to population growth and dietary change.[22]
Between 2010 and 2019, agriculture, forestry and land use contributed between 13% and 21% to global greenhouse gas emissions.[2]Nitrous oxide andmethane make up over half of total greenhouse gas emissions from agriculture.[6]
Substantial land-use change contributions to emissions have been made by Latin America, Southeast Asia, Africa, and Pacific Islands. The area of rectangles shows the region's total emissions in 2019.[24]
Agriculture contributes to greenhouse gas increases through land use in four main ways:
Together, these agricultural processes comprise 54% ofmethane emissions, roughly 80% of nitrous oxide emissions, and virtually all carbon dioxide emissions tied to land use.[25]
Land cover has changed majorly since 1750, as humans havedeforestedtemperate regions. When forests and woodlands are cleared to make room for fields andpastures, thealbedo of the affected area increases, which can result in either warming or cooling effects depending on local conditions.[26] Deforestation also affects regionalcarbon reuptake, which can result in increased concentrations ofCO2, the dominant greenhouse gas.[27] Land-clearing methods such asslash and burn compound these effects, as the burning ofbiomatter directly releases greenhouse gases and particulate matter such assoot into the air. Land clearing can destroy thesoil carbon sponge.[citation needed] Althoughcarbon accounting estimates the greenhouse gas increase when natural land is first farmed, it has been argued that theopportunity cost of land used inefficiently should also be counted to show the importance ofagricultural productivity.[28]
Domesticated livestock constitute almost 60% of mammalbiomass globally.[29]Meat from cattle and sheep have the highest emissions intensity of any agricultural commodity.Greenhouse gas emissions across thesupply chain for different foods
Livestock produces the majority of greenhouse gas emissions from agriculture and demands around 30% of agriculturalfreshwater needs, while only supplying 18% of the globalcalorie intake. Animal-derived food plays a larger role in meeting humanprotein needs, yet is still a minority of supply at 39%, with crops providing the rest.[30]: 746–747 At the same time,livestock farming is affected by climate change.
Out of theShared Socioeconomic Pathways used by theIntergovernmental Panel on Climate Change, only SSP1 offers any realistic possibility of meeting the 1.5 °C (2.7 °F) target.[31] Together with measures like a massive deployment ofgreen technology, this pathway assumes animal-derived food will play a lower role in global diets relative to now.[32] As a result, there have been calls for phasing outsubsidies currently offered to livestock farmers in many places worldwide,[33] andnet zero transition plans now involve limits on total livestock headcounts, including substantial reductions of existing stocks in some countries with extensive animal agriculture sectors like Ireland.[34] Yet, an outright end to human consumption of meat and/or animal products is not currently considered a realistic goal.[35] Therefore, any comprehensive plan ofadaptation to theeffects of climate change, particularly the present and futureeffects of climate change on agriculture, must also consider livestock.[36][37]
Livestock activities also contribute disproportionately to land-use effects, since crops such ascorn andalfalfa are cultivated to feed the animals.[38]
In 2010,enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world.[39] 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.[40] Small ruminants such as sheep and goats contribute approximately 475 million tons of carbon dioxide equivalent to GHG emissions, which constitutes around 6.5% of world agriculture sector emissions.[41] Methane production by animals, principally ruminants, makes up an estimated 15-20% of global production of methane.[42][43]
Worldwide, livestock production occupies 70% of all land used for agriculture or 30% of the land surface of the Earth.[44] The globalfood system is responsible for one-third of the global anthropogenicGHG emissions,[45][46] of which meat accounts for nearly 60%.[47][48]
Cows, sheep and otherruminants digest their food byenteric fermentation, and theirburps are the mainmethane emissions fromland use, land-use change, and forestry: together with methane andnitrous oxide frommanure, this makes livestock the main source of greenhouse gas emissions from agriculture.[49] In addition, manure left on pasture, applied to soil, and treated in management systems together contribute to 7%–10% of global agricultural greenhouse gas emissions.[50]
TheIPCC Sixth Assessment Report in 2022 stated that: "Diets high in plant protein and low in meat and dairy are associated with lower GHG emissions. [...] Where appropriate, a shift todiets with a higher share of plant protein, moderate intake of animal-source foods and reduced intake ofsaturated fats could lead to substantial decreases in GHG emissions. Benefits would also include reduced land occupation and nutrient losses to the surrounding environment, while at the same time providing health benefits and reducing mortality from diet-related non-communicable diseases."[51]
Mean greenhouse gas emissions for different food types[52]
Food Types
Greenhouse Gas Emissions (g CO2-Ceq per g protein)
According to a 2022 study quickly stopping animal agriculture would provide half the GHG emission reduction needed to meet theParis Agreement goal of limiting global warming to 2 °C.[53] There are calls to phase out livestock subsidies as part of ajust transition.[54]
In the context of global GHG emissions, food production within the global food system accounts for approximately 26%. Breaking it down, livestock and fisheries contribute 31%, whereas crop production, land use, and supply chains add 27%, 24%, and 18% respectively to the emissions.[55]
A 2023 study found that avegan diet reduced emissions by 75%.[56]
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 for New Zealand, which is an order of magnitude less than the estimated health system savings from a healthier diet.[57]
Research continues on the use of various seaweed species, in particularAsparegopsis armata, as a food additive that helps reduce methane production in ruminants.[58]
In 2022,greenhouse gas emissions from rice cultivation were estimated at 5.7 billion tonnes CO2eq, representing 1.2% of total emissions.[63] Within the agriculture sector, rice produces almost half the greenhouse gas emissions fromcroplands,[64] some 30% of agriculturalmethane emissions, and 11% of agriculturalnitrous oxide emissions.[65]Methane is released from rice fields subject to long-term flooding, as this inhibits the soil from absorbing atmospheric oxygen, resulting inanaerobic fermentation of organic matter in the soil.[66] Emissions can be limited by planting new varieties, not flooding continuously, and removing straw.[67]
It is possible to cut methane emissions in rice cultivation by improved water management, combining dry seeding and one drawdown, or executinga sequence of wetting and drying. This results in emission reductions of up to 90% compared to full flooding and even increased yields.[68]
Activities such astilling of fields, planting of crops, and shipment of products cause carbon dioxide emissions.[70] Agriculture-related emissions of carbon dioxide account for around 11% of global greenhouse gas emissions.[71] Farm practices such as reducing tillage, decreasing empty land, returningbiomass residue of crops to the soil, and increasing the use of cover crops can reduce carbon emissions.[72]
Methane emissions from agriculture, 2019. Methane (CHa) emissions are measured in tonnes of carbon dioxide-equivalents[73]Global methane budget.
Methane emissions from livestock are the number one contributor to agricultural greenhouse gases globally. Livestock are responsible for 14.5% of total anthropogenic greenhouse gas emissions. One cow alone will emit 220 pounds of methane per year.[74] While theresidence time of methane is much shorter than that of carbon dioxide, it is 28 times more capable of trapping heat.[74] Not only do livestock contribute to harmful emissions, but they also require a lot of land and mayovergraze, which leads to unhealthy soil quality and reduced species diversity.[74] A few ways to reduce methane emissions include switching to plant-rich diets with less meat, feeding the cattle more nutritious food,manure management, andcomposting.[75]
Traditionalrice cultivation is the second biggest agricultural methane source afterlivestock, with a near-term warming impact equivalent to thecarbon dioxide emissions from all aviation.[76] Government involvement in agricultural policy is limited due to the high demand for agricultural products like corn, wheat, and milk.[77] The United States Agency for International Development's (USAID) global hunger and food security initiative, the Feed the Future project, is addressing food loss and waste. By addressing food loss and waste, greenhouse gas emission mitigation is also addressed. By only focusing on dairy systems of 20 value chains in 12 countries, food loss and waste could be reduced by 4-10%.[78] These numbers are impactful and would mitigate greenhouse gas emissions while still feeding the population.[78]
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.[79] While 6% may appear to be a small contribution, nitrous oxide is 300 times more effective at trapping heat per pound than carbon dioxide and has a residence time of around 120 years.[79] Different management practices such as conserving water throughdrip irrigation, monitoring soil nutrients to avoid overfertilization, and usingcover crops in place of fertilizer application may help in reducing nitrous oxide emissions.[80]
Agriculture is often not included in government emissions reduction plans.[81] For example, the agricultural sector is exempt from theEU emissions trading scheme[82] which covers around 40% of the EU greenhouse gas emissions.[83]
Almost 20% of greenhouse gas emissions come from the agriculture and forestry sector.[84] To significantly reduce these emissions, annual investments in the agriculture sector need to increase to $260 billion by 2030. The potential benefits from these investments are estimated at $4.3 trillion by 2030, offering a substantial economic return of 16-to-1.[85]: 7–8
Mitigation measures in the food system can be divided into four categories. These are demand-side changes, ecosystem protections, mitigation on farms, and mitigation insupply chains. On the demand side, limitingfood waste is an effective way to reduce food emissions. Changes to a diet less reliant on animal products such asplant-based diets are also effective.[86]: XXV
With 21% of global methane emissions, cattle are a major driver of global warming.[87]: 6 When rainforests are cut and the land is converted for grazing, the impact is even higher. In Brazil, producing 1 kg of beef can result in the emission of up to 335 kg CO2-eq.[88]Increasing the milk yield of dairy cows has been shown to reduce emissions.[89]Other livestock, manure management and rice cultivation also emit greenhouse gases, in addition to fossil fuel combustion in agriculture.
Important mitigation options for reducing the greenhouse gas emissions from livestock include genetic selection,[90][91] introduction ofmethanotrophic bacteria into the rumen,[92][93] vaccines, feeds,[94] diet modification and grazing management.[95][96][97] Other options are diet changes towardsruminant-free alternatives, such asmilk substitutes andmeat analogues. Non-ruminant livestock, such as poultry, emit far fewer GHGs.[98]
It is possible to cut methane emissions in rice cultivation by improved water management, combining dry seeding and one drawdown, or executing asequence of wetting and drying. This results in emission reductions of up to 90% compared to full flooding and even increased yields.[99]
Reducing the usage ofnitrogen fertilizers throughnutrient management could avoid nitrous oxide emissions equal to 2.77 - 11.48 gigatons of carbon dioxide from 2020 to 2050.[100]
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^Parmar, N.R.; Nirmal Kumar, J.I.; Joshi, C.G. (2015). "Exploring diet-dependent shifts in methanogen and methanotroph diversity in the rumen of Mehsani buffalo by a metagenomics approach".Frontiers in Life Science.8 (4):371–378.doi:10.1080/21553769.2015.1063550.S2CID89217740.
^Martin, C. et al. 2010. Methane mitigation in ruminants: from microbe to the farm scale.Animal 4 : pp 351-365.
^Eckard, R. J.; et al. (2010). "Options for the abatement of methane and nitrous oxide from ruminant production: A review".Livestock Science.130 (1–3):47–56.doi:10.1016/j.livsci.2010.02.010.
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^Gupta, Khushboo; Kumar, Raushan; Baruah, Kushal Kumar; Hazarika, Samarendra; Karmakar, Susmita; Bordoloi, Nirmali (June 2021). "Greenhouse gas emission from rice fields: a review from Indian context".Environmental Science and Pollution Research International.28 (24):30551–30572.Bibcode:2021ESPR...2830551G.doi:10.1007/s11356-021-13935-1.PMID33905059.S2CID233403787.
^Parmar, N.R.; Nirmal Kumar, J.I.; Joshi, C.G. (2015). "Exploring diet-dependent shifts in methanogen and methanotroph diversity in the rumen of Mehsani buffalo by a metagenomics approach".Frontiers in Life Science.8 (4):371–378.doi:10.1080/21553769.2015.1063550.S2CID89217740.
^Martin, C. et al. 2010. Methane mitigation in ruminants: from microbe to the farm scale.Animal 4 : pp 351-365.
^Eckard, R. J.; et al. (2010). "Options for the abatement of methane and nitrous oxide from ruminant production: A review".Livestock Science.130 (1–3):47–56.doi:10.1016/j.livsci.2010.02.010.
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