Mike Huckabee claimed that a single volcanic eruption “will contribute more than 100 years of human activity” toward global warming. This is far from accurate. Humans actually pump upward of 100 times as much carbon dioxide into the atmosphere every year than all the world’s volcanoes combined.

In an interview with Katie Couric of Yahoo News (beginning at the 5:14 mark), the former Arkansas governor and Republican presidential candidate said he thinks “the climate’s been changing over the entire history of the earth.” Couric asked him if he believes that man contributes to global warming. He responded:

Huckabee, July 28: He probably does, but a volcano, in one blast, will contribute more than 100 years of human activity. So when people are worried about it — you know?

Huckabee gives volcanoes far too much credit.

According to a summary of evidence by the U.S. Geological Survey, the entire collection of volcanoes around the world emits an average of 0.26 gigatons of CO2 per year. (A gigaton is equal to one billion metric tons.) Humans today, on the other hand, emit over 30 gigatons every year, from power plants and factories, cars and airplanes, agriculture, and other activities. According to the Energy Information Administration, humans worldwide emitted 32.3 gigatons of CO2 in 2012, the most recent year for which complete data is available.

So that means, humans collectively are responsible for nearly 125 times as much CO2 entering the atmosphere every year as volcanoes.

Among several published studies that yielded the 0.26 gigaton average, the absolute highest possible value was 0.44 gigatons per year, according to the USGS. Even at that extreme end of the range, humans emit more than 73 times as much as volcanoes.

But Huckabee said “in one blast,” so what about when there is a single, large eruption?

The 1991 eruption of Mount Pinatubo, in the Philippines, was one of the largest in modern history. According to the USGS, this eruption released 0.05 gigatons of CO2, or about 50 million metric tons. Again, humans emit more than 30 billion tons of CO2 every year, let alone every 100 years.

Another famously large eruption, the 1980 explosion of Mount St. Helens in Washington, released even less CO2 than Pinatubo, in spite of its fearsome and deadly local impacts. That eruption released only about 0.01 gigatons of CO2, according to the USGS.

As the USGS says (using 2010 CO2 emissions), you would need 700 Pinatubo’s or 3,500 Mount St. Helens’ eruptions, to match a single year of human-caused carbon dioxide emissions. To get to 100 years of human emissions, as Huckabee said? That would take 70,000 Pinatubo or 350,000 Mount St. Helens eruptions.

We asked Huckabee’s campaign if he could provide evidence for his claim; we will update this post if we receive a response.

Though the volcanoes of the world do contribute a reasonable amount to the CO2 in the atmosphere — about the equivalent of New Zealand’s contribution or about half that of the Philippines (its people, not its volcanoes) — their more important contribution in terms of global climate is sulfur dioxide, or SO2. This molecule acts as an aerosol and reflects sunlight away from the earth, helping cool it down.

In other words, Huckabee has it backward: volcanoes actually act to tamp down human-caused warming, not to exacerbate it.

The eruption of Mount Pinatubo in 1991 released an enormous cloud of SO2 — about 20 million tons. This caused the world to cool, not warm, by about half a degree Celsius. Still, though, this can’t match human emissions of SO2, which also comes from smokestacks and other sources. Though emissions have been declining in recent decades, humans still annually emit about 100 million tons of SO2, according to a 2013 study published in the journal Environmental Research Letters.

Volcanic eruptions can be powerful events. They certainly can change the world’s climate — in the cooling direction — in extreme cases. But Huckabee’s claim about their contribution to global warming is little more than hot air.

Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.

– Dave Levitan

Update, Aug. 11: We responded to readers’ questions about volcanic versus human-caused SO2 emissions in our Aug. 11 Mailbag.