Volcanoes emit more CO2 than humans
Global volcanic CO2 emissions are estimated at 0.15 to 0.26 billion metric tons per year. Human fossil fuel burning emits approximately 35 to 37 billion metric tons per year, making human emissions at least 135 times larger.
What we know
Estimates of volcanic CO2 output have been refined over several decades through direct measurement of gas emissions from active volcanoes, submarine venting surveys, and geochemical analysis. The USGS and peer-reviewed studies place total annual volcanic CO2 output at 0.15 to 0.44 billion metric tons, with a preferred estimate around 0.26 billion metric tons per year.
In contrast, global anthropogenic CO2 emissions from fossil fuel combustion and cement production were approximately 36.8 billion metric tons in 2023. The ratio is therefore around 135:1 in favor of human emissions. This comparison was made explicit by geochemist Terry Gerlach (USGS) in a 2011 paper in EOS, noting that anthropogenic emissions clearly dwarf all estimates of volcanic output.
A common misunderstanding conflates short-term volcanic eruptions with ongoing baseline emissions. Large eruptions like Pinatubo in 1991 actually caused temporary global cooling by injecting sulfate aerosols into the stratosphere that reflected sunlight. Even the CO2 from major eruptions adds only marginally to the ongoing human-emitted total. The isotopic signature of atmospheric CO2 also confirms its biogenic fossil fuel origin: volcanic CO2 has different carbon isotope ratios than fossil-derived CO2, and the measured atmospheric trend matches the fossil fuel signature.
Common claims
- Volcanic eruptions release more CO2 than humansFalse - humans emit at least 135 times more CO2 annually
- We cannot measure volcanic CO2 accuratelyFalse - direct measurement and geochemistry give consistent estimates
- Major eruptions release huge amounts of CO2Partially true but small - a major eruption adds a fraction of one year's human output