Agriculture contributes towards climate change through greenhouse gas emissions and by the conversion of non-agricultural land such as forests into agricultural land. The agriculture, forestry and land use sector contribute between 13% and 21% of global greenhouse gas emissions. Emissions of nitrous oxide, methane make up over half of total greenhouse gas emission from agriculture. Animal husbandry is a major source of greenhouse gas emissions.
The agricultural food system is responsible for a significant amount of greenhouse gas emissions. In addition to being a significant user of land and consumer of fossil fuel, agriculture contributes directly to greenhouse gas emissions through practices such as rice production and the raising of livestock. The three main causes of the increase in greenhouse gases observed over the past 250 years have been fossil fuels, land use, and agriculture. Farm animal digestive systems can be put into two categories: monogastric and ruminant. Ruminant cattle for beef and dairy rank high in greenhouse-gas emissions; monogastric, or pigs and poultry-related foods, are low. 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. Furthermore, CO2 is actually re-emitted into the atmosphere by plant and soil respiration in the later stages of crop growth, causing more greenhouse gas emissions. The amount of greenhouse gases produced during the manufacture and use of nitrogen fertilizer is estimated as around 5% of anthropogenic greenhouse gas emissions. The single most important way to cut emissions from it is to use less fertilizers, while increasing the efficiency of their use.
There are many strategies that can be used to help soften the effects, and the further production of greenhouse gas emissions - this is also referred to as climate-smart agriculture. Some of these strategies include a higher efficiency in livestock farming, which includes management, as well as technology; a more effective process of managing manure; a lower dependence upon fossil-fuels and nonrenewable resources; a variation in the animals' eating and drinking duration, time and location; and a cutback in both the production and consumption of animal-sourced foods. A range of policies may reduce greenhouse gas emissions from the agriculture sector for a more sustainable food system.
Agricultural activities emit the greenhouse gases carbon dioxide, nitrous oxide, and methane.
Carbon dioxide emissions come from things such as tilling of fields, planting of crops, and even the shipment of crops or food cultivated to markets for revenue. Agricultural related emissions of carbon dioxide account for around 11% of the global greenhouse gas emissions. To help mitigate carbon dioxide emissions farm practices such as reduce tillage, decrease in empty land, return biomass residue of crop to soil, and increase use of cover crops can be promoted.
Methane emissions come from livestock such as cows belching and are the number one contributor to agricultural greenhouse gases globally. Every year one cow alone will emit 220 pounds of methane methane making 14.5% of greenhouse gas emissions. While the residence time of methane is much shorter than that of carbon dioxide its potency is 28 times stronger its contribution to warming. Not only does livestock contribute to harmful emissions but they also require a lot of land and may overgraze which leads to unhealthy soil quality and reduced species diversity. A few ways to reduce methane emissions includes consumption of plant-rich diets with less meat, feeding the cattle more nutritious food, manure management, and composting.
Traditional rice cultivation is the second biggest agricultural methane source after livestock, with a near-term warming impact equivalent to the carbon-dioxide emissions from all aviation. Government involvement in agricultural policy is limited due to high demand for agricultural products like corn, wheat, and milk. The United States Agency for International Development's (USAID) global hunger and food security initiative, 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%. These numbers are impactful and would mitigate greenhouse gas emissions while still feeding the population.
Nitrous oxide emission comes from the increased use of synthetic and organic fertilizers. Fertilizers increase crop yield production and allows the crops to grow at a faster rate. Agriculture emissions of nitrous oxide is 6% of the greenhouse gas emission in the United States and has increased in concentration by 30% since 1980. While 6% may appear to be a small contributor, per pound nitrous oxide is 300 times more powerful than carbon dioxide emissions and has a residence time of around 120 years. Different management practice such as water conservation through drip irrigation, nutrient monitoring to avoid overfertilization, and the use of a cover crop in place of fertilizer application may help in reducing level of nitrous oxide emissions.
Agriculture contributes to greenhouse gas increases through land use in four main ways:
Together, these agricultural processes comprise 54% of methane emissions, roughly 80% of nitrous oxide emissions, and virtually all carbon dioxide emissions tied to land use.
The planet's major changes to land cover since 1750 have resulted from deforestation in temperate regions: when forests and woodlands are cleared to make room for fields and pastures, the albedo of the affected area increases, which can result in either warming or cooling effects, depending on local conditions. Deforestation also affects regional carbon reuptake, which can result in increased concentrations of CO2, the dominant greenhouse gas. Land-clearing methods such as slash and burn compound these effects by burning biomatter, which directly releases greenhouse gases and particulate matter such as soot into the air. Land clearing can destroy the soil carbon sponge.
See also: Environmental impact of animal agriculture § Greenhouse gas emissions
Livestock and livestock-related activities such as deforestation and increasingly fuel-intensive farming practices are responsible for over 18% of human-made greenhouse gas emissions, including:
Livestock activities also contribute disproportionately to land-use effects, since crops such as corn and alfalfa are cultivated in order to feed the animals.
In 2010, enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world. 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. Methane production by animals, principally ruminants, is estimated 15-20% global production of methane.
Worldwide, livestock production occupies 70% of all land used for agriculture, or 30% of the land surface of the Earth. The way livestock is grazed also affects future fertility of the land. Not circulating grazing can lead to unhealthy compacted soils. The expansion of livestock farms affects the habitats of native wildlife and has led to their decline.
It has been suggested that livestock subsidies be phased out in a just transition.
Large scale farming can cause large amounts of soil erosion, causing between 25 and 40 percent of soil to reach water sources, with it carrying the pesticides and fertilizers used by farmers, thus polluting bodies of water further. The trend to constantly bigger farms has been highest in United States and Europe, due to financial arrangements, contract farming. Bigger farms tend to favour monocultures, overuse water resources, accelerate the deforestation and a decline in soil quality. A study from 2020 by the International Land Coalition, together with Oxfam and World Inequality Lab found that 1% of the land owners manage 70% of the world's farmland. The highest discrepance can be found in Latin America: The poorest 50% own just 1% of the land. Small landowners, as individuals or families, tend to be more cautious in land use. As of 2020, however, the proportion of small landowners has been decreasing since the 1980s. Currently, the largest share of smallholdings can be found in Asia and Africa.
Between 2010 and 2019, agriculture, forestry and land use contributed between 13% and 21% to global greenhouse gas emissions. Emissions of nitrous oxide, methane make up over half of total greenhouse gas emission from agriculture.
In 2020, it was estimated that the food 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.
In 2010, agriculture, forestry and land-use change were estimated to contribute 20–25% of global annual emissions.
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Agriculture is often not included in government emissions reductions plans. For example, the agricultural sector is exempt from the EU emissions trading scheme which covers around 40% of the EU greenhouse gas emissions.
Several mitigation measures for use in developed countries have been proposed: 
The Intergovernmental Panel on Climate Change (IPCC) has reported that agriculture is responsible for over a quarter of total global greenhouse gas emissions. Given that agriculture's share in global gross domestic product (GDP) is about 4%, these figures suggest that agricultural activities produce high levels of greenhouse gases. Innovative agricultural practices and technologies can play a role in climate change mitigation and adaptation. This adaptation and mitigation potential is nowhere more pronounced than in developing countries where agricultural productivity remains low; poverty, vulnerability and food insecurity remain high; and the direct effects of climate change are expected to be especially harsh. Creating the necessary agricultural technologies and harnessing them to enable developing countries to adapt their agricultural systems to changing climate will require innovations in policy and institutions as well. In this context, institutions and policies are important at multiple scales.
Travis Lybbert and Daniel Sumner suggest six policy principles:
State- or NGO-sponsored projects can help farmers be more resilient to climate change, such as irrigation infrastructure providing a dependable water source as rains become more erratic. Water catchment systems that collect water during the rainy season to be used during the dry season or periods of drought, can also be used to mitigate the effects of climate change. Some programs, like Asociación de Cooperación para el Desarrollo Rural de Occidente (C.D.R.O.), a Guatemalan program funded by the United States’ government until 2017, focus on agroforestry and weather monitoring systems to help farmers adapt. The organization provided residents with resources to plant new, more adaptable crops to alongside their typical maize to protect the corn from variable temperatures, frost, etc. C.D.R.O. also set up a weather monitoring system to help predict extreme weather events, and would send residents text messages to warn them about periods of frosts, extreme heat, humidity, or drought. Projects focusing on irrigation, water catchment, agroforestry, and weather monitoring can help Central American residents adapt to climate change.
The Agricultural Model Intercomparison and Improvement Project (AgMIP) was developed in 2010 to evaluate agricultural models and intercompare their ability to predict climate impacts. In sub-Saharan Africa and South Asia, South America and East Asia, AgMIP regional research teams (RRTs) are conducting integrated assessments to improve understanding of agricultural impacts of climate change (including biophysical and economic impacts) at national and regional scales. Other AgMIP initiatives include global gridded modeling, data and information technology (IT) tool development, simulation of crop pests and diseases, site-based crop-climate sensitivity studies, and aggregation and scaling.
One of the most important projects to mitigate climate change with agriculture and adapting agriculture to climate change at the same time, was launched in 2019 by the "Global EverGreening Alliance". The initiative was announced in the 2019 UN Climate Action Summit. One of the main methods is Agroforestry. Another important method is Conservation farming. One of the targets is to sequester carbon from the atmosphere. By 2050 the restored land should sequestrate 20 billion of carbon annually. The coalition wants, among other, to recover with trees a territory of 5.75 million square kilometres, achieve a health tree - grass balance on a territory of 6.5 million square kilometres and increase carbon capture in a territory of 5 million square kilometres.
The first phase is the "Grand African Savannah Green Up" project. Already millions families implemented these methods, and the average territory covered with trees in the farms in Sahel increased to 16%.
Climate-smart agriculture (CSA) (or climate resilient agriculture) is an integrated approach to managing landscapes to help adapt agricultural methods, livestock and crops to the effects of climate change and, where possible, counteract it by reducing greenhouse gas emissions from agriculture, at the same time taking into account the growing world population to ensure food security. Thus, the emphasis is not simply on carbon farming or sustainable agriculture, but also on increasing agricultural productivity. "CSA ... is in line with FAO’s vision for Sustainable Food and Agriculture and supports FAO’s goal to make agriculture, forestry and fisheries more productive and more sustainable".CSA has three pillars: increasing agricultural productivity and incomes; adapting and building resilience to climate change; and reducing or removing greenhouse gas emissions from agriculture. CSA lists different actions to counter the future challenges for crops and plants. With respect to rising temperatures and heat stress, e.g. CSA recommends the production of heat tolerant crop varieties, mulching, water management, shade house, boundary trees and appropriate housing and spacing for cattle. There are attempts to mainstream CSA into core government policies, expenditures and planning frameworks. In order for CSA policies to be effective, they must be able to contribute to broader economic growth, the sustainable development goals and poverty reduction. They must also be integrated with disaster risk management strategies, actions, and social safety net programmes.
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