Which natural source is the largest emitter of methane on Earth?

The largest natural source of methane on Earth is wetlands. Waterlogged soils contain little oxygen, creating ideal conditions for methanogens—microorganisms that produce methane while breaking down organic matter. The gas can then travel through soil, open water, or plant tissues into the atmosphere.

Wetlands include marshes, swamps, peatlands, floodplains, and other saturated environments. They are estimated to contribute roughly 20–30% of atmospheric methane, although the exact figure varies with climate, geography, season, and how emissions are measured. Wetland methane is part of the natural carbon cycle, but warming and altered rainfall can increase emissions in some regions.

Forests are not usually counted as the largest direct natural methane source, and oceans release methane through sediments and other processes but generally contribute less than wetlands. Termites emit methane during digestion, yet their global contribution is smaller. Human activities—including livestock, rice cultivation, landfills, and fossil-fuel production—also release large amounts, but those are anthropogenic rather than natural sources.