How do volcanoes replenish carbon dioxide in Earth’s atmosphere?

Volcanoes replenish carbon dioxide in Earth’s atmosphere through the process of volcanic outgassing, which releases gases stored within magma. As magma rises toward the surface, decreasing pressure allows dissolved gases—including carbon dioxide, water vapor, and sulfur dioxide—to separate and escape into the atmosphere through volcanoes, fumaroles, and vents in rift or subduction zones.1234

On geologic timescales, this process is a critical component of the geologic carbon cycle. Carbon that has been sequestered in the Earth's crust—often through the burial of carbonate sediments or organic matter—is returned to the atmosphere when that material is subjected to deep burial, melting, and subsequent volcanic activity. While individual eruptions contribute relatively small amounts of carbon dioxide compared to modern human activities, long-term variations in volcanic and tectonic activity have historically played a significant role in regulating atmospheric chemistry and global climate.534