Where do methane emissions come from?

The fossil fuel sector emits methane at several stages of extraction, processing and distribution.

• 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 and where maintenance is difficult.
• Processing and storage. Natural gas is primarily methane. Inadequate or faulty equipment leads to leaks and to unintended venting.
• Transportation. Methane is moved through pipelines and storage facilities, where damage, corrosion or poor maintenance causes leaks.

Coal combustion itself does not produce methane, but mining can be a significant source.

• Underground coal mining. Coal seams naturally contain methane, which is released when coal is mined unless it is captured.
• Coal bed methane. Methane trapped within coal deposits is sometimes captured as a byproduct for energy, and otherwise escapes.
• Ventilation in mines. Inadequate ventilation or outdated gas capture systems result in significant leakage.

The agricultural sector is a significant source of methane, from several activities.

• Enteric fermentation. Ruminant animals such as cattle, sheep and goats produce methane during digestion, released primarily through belching rather than flatulence.
• Manure management. Manure stored or treated with limited oxygen, for example in anaerobic lagoons or storage pits, generates methane as it decomposes.
• Rice cultivation. Flooded rice paddies create the anaerobic conditions in which methanogenic bacteria produce methane.
• Other agricultural practices. Decaying crop residues and soil organic matter contribute under some conditions, though less than livestock and rice.

The waste and wastewater sector emits methane primarily through the anaerobic decomposition of organic matter.

• Landfills. Organic waste such as food scraps, paper and yard waste breaks down under low-oxygen conditions and produces methane. Many landfills now have gas capture systems, but not all emissions are contained.
• Open dump landfills. Where waste management is less regulated, open dumps without covering or gas collection release methane directly to the atmosphere.
• Wastewater treatment. Organic material decomposes and releases methane during sewage treatment, particularly in anaerobic digesters and sludge treatment ponds. Some facilities capture this methane for energy.