Do Volcanoes Generate More Greenhouse Gas Than Humans?

Is the rumor about volcanoes and greenhouse gases true? Not even close

Icelandic volcano in eruption
Jon Vidar Sigurdsson/Nordic Photos/Getty Images

This argument that human-caused carbon emissions are merely a drop in the bucket compared to greenhouse gases generated by volcanoes has been making its way around the rumor mill for years. And while it may sound plausible, the science just doesn’t back it up.

According to the U.S. Geological Survey (USGS), the world’s volcanoes, both on land and undersea, generate about 200 million tons of carbon dioxide (CO2) annually, while our automotive and industrial activities cause some 24 billion tons of CO2 emissions every year worldwide. Despite the arguments to the contrary, the facts speak for themselves: carbon dioxide emissions from volcanoes comprise less than one percent of those generated by today’s human endeavors.

Human Emissions Also Dwarf Volcanoes in Carbon Dioxide Production

Another indication that human emissions dwarf those of volcanoes is the fact that atmospheric CO2 levels, as measured by sampling stations around the world set up by the federally funded Carbon Dioxide Information Analysis Center, have gone up consistently year after year regardless of whether or not there have been major volcanic eruptions in specific years. “If it were true that individual volcanic eruptions dominated human emissions and were causing the rise in carbon dioxide concentrations, then these carbon dioxide records would be full of spikes—one for each eruption,” says Coby Beck, a journalist writing for online environmental news portal “Instead, such records show a smooth and regular trend.”

Do Volcano Eruptions Cause Global Cooling?

The IPCC's 5th Assessment Report on climate change evaluated the effects of sulfur dioxide (SO2) injections in the atmosphere by volcanoes. It turns out that even during large volcanic eruptions, not enough SO2 reached the stratosphere to create a strong climate change effect - and if it did, it would actually cool the atmosphere. SO2 converts to sulfuric acid aerosol when it hits the stratosphere and can exercise a cooling effect long after a volcanic eruption has taken place. Some scientists believe that spectacular volcanic eruptions, like that of Mt. St. Helens in 1980 and Mt. Pinatubo in 1991, actually lead to short-term global cooling as sulfur dioxide and ash in the air and stratosphere reflect some solar energy instead of letting it into Earth’s atmosphere.

Scientists tracking the effects of the major 1991 eruption of the Philippines’ Mt. Pinatubo found that the overall effect of the blast was to cool the surface of the Earth globally by some 0.5 degrees Celsius a year later, even though rising human greenhouse gas emissions and an El Nino event caused some surface warming during the 1991-1993 study period.

Volcanoes May Melt Antarctic Ice Caps from Below

In an interesting twist on the issue, British researchers published an article in the peer reviewed scientific journal Nature showing how volcanic activity may be contributing to the melting of ice caps in Antarctica—but not because of any emissions, natural or man-made, per se. Instead, scientists Hugh Corr and David Vaughan of the British Antarctic Survey believe that volcanoes underneath Antarctica may be melting some of the continent’s ice sheets from below, just as warming air temperatures from human-induced emissions erode them from above.

Edited by Frederic Beaudry.