Natural gas methane, also known as fossil methane, is a naturally occurring greenhouse gas that is emitted in large quantities during human activities such as oil and gas extraction, processing, storage, and distribution. When natural gas or crude oil is extracted from the Earth, methane leaks can occur via unintentional releases that go unchecked due to the lack of appropriate infrastructure.

In addition, human-created emissions come from sources including landfills, livestock flatulence, rice farming, the combustion of forest biomass, as well as wastewater treatment. Natural sources include wetlands and thawing permafrost due to climate change.