What Causes More Climate Change - Humans Or Volcanic Eruptions?


Robin Andrews

Science & Policy Writer

Stromboli, one of the most active volcanoes in the world, backlit by a full moon. Rainer Albiez/Shutterstock

We’ve noticed that under a lot of our climate change articles, a common argument used by deniers of the science keeps rearing its ugly head. Namely, volcanic eruptions dump more carbon dioxide into the atmosphere than humans ever could, so our own greenhouse gas (GHG) emissions have almost no influence on the climate whatsoever.

A similar argument posits that volcanic eruptions produce so much reflective sulfur dioxide that when one erupts badly enough, it’ll cool the climate so much that all our GHGs will be canceled out in the future. Both of these arguments hold zero water. They are bullshit, and here’s your primer explaining why.


Let’s look at the former argument first, the idea that volcanoes are better producers of carbon dioxide than humanity.

Firstly, yes, it’s true that volcanoes produce more carbon dioxide than most other processes. They actually release plenty of gases – technically known as volatiles – whose concentrations depend on the style of the eruption (sudden and explosive versus prolonged and calm) and the geochemistry of the magma source.

The most common gases released are water vapor, carbon dioxide, carbon monoxide, hydrogen sulfide compounds, sulphur dioxide, and a handful of others.

Humans will always produce more carbon dioxide per year than volcanoes. cornfield/Shutterstock

Climate skeptics often point to water vapor being the most important GHG, but this is normally used to suggest that carbon dioxide isn’t a problem. Water vapor does trap solar radiation into the atmosphere, but its concentration directly depends on the temperature. Warmer worlds have more water vapor in the atmosphere, and colder worlds have less. We cannot control this.


Carbon dioxide, however, we do control. Although not the most effective trapper of heat, it is still pretty good at it; its cumulative lifetime up there is around 20 to 200 years. This makes it the most important GHG.

Volcanoes release a fair amount of it. Sometimes they release so much that it causes mass extinctions. The Siberian Traps, the volcanic province that produced a continental-sized lava flow over 1 million years, 252 million years back. This released 85 trillion tonnes of carbon dioxide, triggering a roughly 6-8°C (10.8-14.4°F) rise in global temperatures in a very short space of time.

This likely triggered the Great Dying, a mass extinction that wiped out as much as 96 percent of all life on Earth. It was as close to the apocalypse as you’re going to get.

But this event, although unique, even if it happened today would pale in comparison to the amount of carbon dioxide humanity pumped into the sky every single year – and that’s the crux of it. It’s all about the rate of carbon dioxide emitted over time, not the absolute amounts, per se.


The Siberian Traps produced a lot of carbon dioxide over a geologically short period of time, but humans produce even more in what amounts to be a geological blink of an eye. On average, per year, volcanoes emit 0.3 billion tonnes of carbon dioxide. Humans produce at least 100 times that, and that amount is rising year on year.

In fact, at no point in the last century has a volcanic eruption produced more carbon dioxide than there already is in the atmosphere. As for the future, there is no natural process in which a volcano would emit more carbon dioxide than we can over the course of a year. So this argument will never be correct.

As for the second point, yes, it is also true that volcanoes produce a lot of sulfur dioxide. When this readily reacts with water vapour in our atmosphere, it turns into clumps of sulfuric acid. It’s a reflective substance, which means the more of it there is in the atmosphere, the less solar radiation makes it through and the cooler the Earth will be.

(Incidentally, some geoengineers suggest that we could pump tonnes of sulfur dioxide into the sky in order to offset the man-made warming. While this may work, it would also merely mask the problem rather than deal with the direct cause of it – and let’s not forget about the potentially dangerous acid rain that all that sulfur would turn into, as well as all the other ways in which such a program would potentially alter the climate. Best leave it, we say.)

The sulfur dioxide is more of a game changer than the carbon dioxide in the short-term. Gardar Olafsson/Shutterstock

In terms of volcanic emissions, these aerosols do have a more noticeable effect on our climate. When Mount Pinatubo erupted in 1991, global temperatures cooled by a fraction of a degree for several months.

When the far more explosive Tambora eruption took place in 1815, so much sulfur was released that 1816, in many parts of the world, lacked any significantly warm months whatsoever. In fact, that was dubbed The Year Without Summer.

Before all that carbon dioxide could take effect during the Great Dying, the 75 trillion tonnes of sulfur aerosols released by the Siberian Traps actually helped to blot out the Sun for several decades at least. The planet entered a snap freeze, photosynthesis in parts of the world stalled, and food chains across the world started to collapse.

The most notable effect sulfur aerosols have ever had was probably during the formation of the most prominent Snowball Earth. Around 700-800 million years ago, there was a single supercontinent named Rodinia – Russian for “The Motherland.” When supercontinents have been assembled, carbon dioxide-effusing  eruptions are generally rarer, which means there's not much to offset any massive sulfur dioxide discharges.


So, when a range of volcanoes 3,220 kilometers (2,000 miles) long erupted, the aerosols managed to block out so much sunlight for so long that for perhaps hundreds of millions of years after that, glaciers spread from the poles to the equator, and from a distance, the Earth looked like a giant snowball.

These are the extremes – and again, this sulfur is emitted over a very long timescale. If an eruption like that happened today, the warming effect of the GHGs would overpower the sulfur without a doubt.

In short, we are simply producing too much carbon dioxide, which renders both arguments null and void. Consider these myths debunked.

We are more powerful than volcanoes. Congratulations? SergeyIT/Shutterstock


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