How do volcanoes return carbon dioxide from Earth’s interior to the atmosphere?

Volcanoes return carbon dioxide to the atmosphere through the process of volcanism, which acts as a key mechanism in the geologic carbon cycle.

Carbon is stored within Earth's crust in various forms, such as limestone and organic matter found in sediments. When these materials are buried deep within the Earth, they can undergo melting due to intense heat and pressure. This process releases carbon dioxide from the molten rock, or magma.4

As magma rises toward the surface, carbon dioxide—which is less soluble in magma than other volcanic gases—begins to separate from the melt at significant depths. This gas is then emitted into the atmosphere through:1

• Volcanic eruptions: Explosive events that vent gases directly into the air.12
• Fumaroles: Vents that allow volcanic gases to leak from magma chambers located beneath the surface.13
• Rift and subduction zones: Tectonic regions where volcanic activity and related phenomena facilitate the release of carbon dioxide from the Earth's interior.23

Once released, this carbon dioxide becomes part of the atmospheric chemistry, influencing global climate over geologic timescales.23