Where do methane emissions come from?

Not all methane emissions are human-caused.

60% of methane emissions are due to human activity - mostly from fossil fuels, waste and agriculture

Emissions from human activities

2020 emissions from human activity and the contribution from different sectors, as estimated by the Global Methane Budget.

Fossil fuels

The fossil fuel sector contributes to methane emissions through various stages of resource extraction, processing, and distribution. Here’s a brief overview:

  • Extraction: During the drilling of oil and natural gas wells, methane can leak from equipment, seals, and other infrastructure. This is especially common in older fields or where maintenance is challenging.

  • Processing and Storage: Once extracted, natural gas (which is primarily methane) is processed and stored. Inadequate equipment or faulty infrastructure can lead to leaks and unintended venting of methane.

  • Transportation: Methane is transported via pipelines and storage facilities. Damage, corrosion, or poor maintenance of these systems can result in leaks during distribution.

While coal combustion itself does not produce methane, the mining process can be a significant source of methane emissions:

  • Underground Coal Mining: Coal seams naturally contain methane. When coal is mined, especially in underground operations, methane is released into the atmosphere if not properly captured.

  • Coal Bed Methane: This is methane trapped within coal deposits. In some cases, it is captured as a byproduct for energy production, but if not managed, it can escape into the atmosphere.

  • Ventilation in Mines: Inadequate ventilation or outdated gas capture systems in coal mines can result in significant methane leakage.

Agriculture

The agricultural sector is a significant source of methane emissions, stemming from several key activities:

  • Enteric Fermentation: Ruminant animals (such as cattle, sheep, and goats) naturally produce methane during digestion. This process, known as enteric fermentation, results in methane being released primarily through burping (not farting as commonly believed).

  • Manure Management: When animal manure is stored or treated in environments with limited oxygen—such as anaerobic lagoons or storage pits—methane is generated as a byproduct of the decomposition process.

  • Rice Cultivation: Flooded rice paddies create anaerobic conditions that encourage methanogenic bacteria to produce methane. The standing water in these fields facilitates the production and release of the gas.

  • Other Agricultural Practices: Decaying crop residues and organic matter in soils under certain conditions can also contribute to methane emissions, though these sources are generally less significant than those from livestock and rice production.

Waste

The waste and wastewater sector contributes to methane emissions primarily through the anaerobic decomposition of organic matter. Here’s a brief overview:

  • Landfills: Organic waste—such as food scraps, paper, and yard waste—breaks down in landfills under low-oxygen conditions. This anaerobic decomposition produces methane. Although many landfills now incorporate gas capture systems, not all emissions are effectively contained.

  • Open Dump Landfills: In regions where waste management is less regulated, open dump sites are common. Without proper covering or gas collection systems, methane generated from decomposing waste escapes directly into the atmosphere.

  • Wastewater Treatment: During sewage treatment, particularly in anaerobic digesters and sludge treatment ponds, organic materials decompose and release methane. Some facilities capture and use this methane for energy, but many systems still release it into the atmosphere.

Natural emissions

A substantial portion of total methane emissions, approximately 40% , come from natural sources. The three main natural sources of methane in the present climate system are wetlands (e.g., bogs, marshes, peatlands, swamps), freshwaters, and geological outgassing (e.g., gas-oil seeps, volcanoes, microseepage) .

Methane is mainly removed from the air by a natural cleaning process that happens in the lower layers of our atmosphere, a process known as oxidation. This process depends on the amounts of methane and other gases present; when too much methane is released, the air’s ability to clean itself slows down, letting methane stay in the atmosphere for a longer time.

Natural sources like wetlands and melting permafrost can release more methane as the planet warms due to human activity, which blurs the distinction between natural and human-caused methane sources.

When researchers try to project how the climate will change, they have to make judgements about how the emissions of different gases, including methane will evolve in the future. The standard approach is to assume that natural methane emissions will not increase in the future, but rather stay constant as the world warms, in part because of the substantial uncertainty on how natural methane emissions will change. So, if natural methane emissions increase under climate change then the future warming from methane may be underestimated. There is evidence that some of the recent rapid increase in atmospheric methane concentrations may have been fuelled by wetland emissions (Oh et al., 2022; Peng et al., 2022; Qu et al., 2022; Shindell et al., 2024).