Volcanoes emit more carbon dioxide than humans

Volcanoes emit more carbon dioxide than humans
	FALSE
	"Volcanoes, including undersea volcanoes, release more carbon dioxide than all human activities combined, so human emissions cannot be the main cause of climate change."
Domain	Science & Environment
Tactic	Statistical & Evidentiary Distortion;
Era	Current
First seen	2009
Origin	Claims by critics of climate science, popularized in books and online commentary around 2009
Last reviewed	2026-10-26
	Further reading: books on Science & Environment

The claim that volcanoes emit more carbon dioxide than humans is a persistent argument against human-caused climate change. It is false by a very wide margin. Scientific estimates indicate that volcanoes on land and under the sea together release roughly 0.3 to 0.4 billion tonnes of carbon dioxide a year. Human activities, mainly burning fossil fuels and making cement, release more than 35 billion tonnes a year. Humans emit roughly 100 times more carbon dioxide than all of the world's volcanoes combined.

The claim

The claim takes several forms: that a single large eruption releases more carbon dioxide than humans have released in all history; that volcanoes, including thousands of undersea volcanoes, emit more carbon dioxide each year than humans do; or that volcanic activity, rather than fossil fuels, explains rising carbon dioxide levels.

Origin

The argument has circulated in various forms for decades. It gained wider attention after 2009, when it appeared in a popular book by the Australian geologist and mining executive Ian Plimer, Heaven and Earth, which was criticized by climate scientists for numerous errors. Since then it has been repeated in opinion columns, speeches, social media posts and memes, often illustrated with dramatic images of erupting volcanoes.

What the evidence shows

Volcanologists measure volcanic carbon dioxide emissions in several ways, including direct gas sampling at volcanic vents, satellite and ground-based monitoring of gas plumes, and estimates of the carbon released at mid-ocean ridges and from volcanic areas that leak gas without erupting.

In a widely cited 2011 review in the American Geophysical Union's newsletter Eos, the US Geological Survey volcanologist Terrance Gerlach estimated that the world's volcanoes emit between about 0.13 and 0.44 billion tonnes of carbon dioxide a year. More recent estimates by the Deep Carbon Observatory, an international research program, put total volcanic emissions at around 0.3 to 0.4 billion tonnes a year.

By contrast, human activities emitted more than 37 billion tonnes of carbon dioxide from fossil fuels and industry in 2023, according to the Global Carbon Project, with additional emissions from land-use change such as deforestation. That is roughly 100 times the volcanic total.

Even very large eruptions do not change this picture. The 1991 eruption of Mount Pinatubo in the Philippines, one of the largest of the twentieth century, released roughly 0.05 billion tonnes of carbon dioxide, a few hours' to a day's worth of current human emissions. Its main climate effect was actually cooling: the sulfur dioxide it released formed particles in the upper atmosphere that reflected sunlight and lowered global temperatures by about half a degree Celsius for a year or two.

Other evidence also rules out volcanoes as the cause of rising carbon dioxide. Carbon from fossil fuels has a distinctive chemical signature: it lacks the radioactive isotope carbon-14 and is relatively low in carbon-13. As atmospheric carbon dioxide has risen, the proportion of these isotopes has shifted exactly as expected if the extra carbon comes from burning fossil fuels. Atmospheric oxygen has also declined slightly, consistent with combustion. And the rise in carbon dioxide has been smooth and steady, tracking human emissions, rather than jumping after major eruptions.

Why it persists

Visual power. Erupting volcanoes are dramatic and look enormous compared with a car exhaust pipe or a power station chimney.
Hidden sources. Claims about thousands of unseen undersea volcanoes sound plausible because few people know how they are measured.
Scale is counterintuitive. Human emissions come from billions of small and large sources running constantly, which add up to far more than occasional eruptions.

Lessons for readers

Ask for the numbers. Claims about which source is "bigger" can be checked against published measurements.
A dramatic image is not a measurement.
When a claim conflicts with several independent lines of evidence, such as isotope measurements, oxygen levels and the timing of changes, it is very unlikely to be correct.

Sources

Terrance Gerlach, "Volcanic versus anthropogenic carbon dioxide," Eos, Transactions American Geophysical Union 92, no. 24 (2011).
US Geological Survey, Volcano Hazards Program, "Volcanoes Can Affect Climate."
Deep Carbon Observatory, Deep Carbon Observatory: A Decade of Discovery (2019).
Global Carbon Project, Global Carbon Budget 2023.