05 Dec 2012, Russia --- Tolbachik Volcano erupting, Kamchatka, Russia --- Image by © Sergey Gorshkov/Minden Pictures/Corbis

There have been many sources to falsely claim that volcanic activity releases more greenhouse gases into the atmosphere than current emissions by humans, but this is simply not true.

To clarify, I am not stating that volcanic activity has absolutely no effect on our global climate, and in fact volcanic eruptions usually have a net cooling effect due to the release of sulfate aerosols, which tends to reflect incoming solar radiation. To understand the role volcanic activity plays in shaping global climate, it would stand to reason that we first need to understand what comes spewing out of these geologic spectacles.

Volcanic Emissions

When typically thinking of a volcanic eruption, the first thing that might come to mind is a plume of smoke and rivers of boiling hot magma that slowly engulf everything in it’s path. However, there are actually two different types of eruptions which contribute to how the insides of the Earth are delivered to the surface. Effusive eruptions are low energy eruptions which slowly push magma out of a volcanoes crater as a plume of smoke menacingly grows overhead. Explosive eruptions, on the other hand, are just that: explosive! These eruptions are high in energy, and tend to launch debris and aerosols to high altitudes as magma violently exits the crater. No matter, whether the eruption is effusive or explosive, ultimately the same types of material are being emitted. For now, we won’t get into the nitty-gritty geology of volcanoes and how they differ, because what we really care about right now are the agents which affect global climate.

So what else besides CO2 is released from a volcanic eruption?

By far, the most abundant gas released from a volcanic eruption is water vapor (H2O), followed by carbon dioxide (CO2) and sulfur dioxide (SO2). A host of trace gases are also released, including: carbon monoxide (CO), hydrogen sulfide (H2S), carbonyl sulfide (COS), carbon disulfide (C2S), hydrogen chloride (HCL), hydrogen (H), methane (CH4), hydrogen fluoride (HF), hydrogen bromine (HBr), Mercury vapor (Hg), and even gold in some cases. These trace gases, by definition,  each make up less than 1% of the total volume of gases emitted.

We know that both carbon dioxide and water vapor are very strong greenhouse gases, because of their ability to retain infrared radiation (heat). If you happen to live nearby an active volcano, or have had the opportunity to experience an eruption, it’s easy to perceive that the amount of “stuff” thrown into the atmosphere by a single eruption must challenge or equal the volume of carbon dioxide and other greenhouse gases emitted by humans. In reality though, even when considering  deep sea hydrothermal venting, this is just not the case.

By the Numbers

According to research carried out by the USGS (United States Geological Survey), in cooperation with international agencies, volcanologists were able to calculate the average CO2 output from volcanoes and deep sea hydrothermal vents worldwide. Annually, volcanoes around the world release approximately 200 million tonnes of CO2. While this may sound like a whole lot, let’s put this into perspective: Global CO2 emissions from fossil fuels alone come in at a staggering 33.8 billion tonnes/year, according to data from 2013. That figure doesn’t include emissions from other sources like cement production, deforestation, or even agriculture! This means that volcanic emissions make up less than 1 percent of global carbon dioxide emissions.

volcanic emissions make up less than 1 percent of global carbon dioxide emissions.

Now you may be wondering, “what about that other greenhouse gas, water vapor?” This is would be a very reasonable counter argument, considering it’s the dominant gas released during a volcanic eruption. To answer this simply, I will say that while water vapor is a potent greenhouse gas, it has a much shorter residence time within Earth’s atmosphere when compared to CO2. Moreover, water vapor is considered an amplifier of greenhouse gases and is directly related to temperature, which can create a positive feedback loop. For example, as global temperatures increase from an abundance of CO2, more water is evaporated into the atmosphere, warming the atmosphere more as excessive heat is retained by the additional water vapor. This means that for any change within our global climate system, like the addition of otherwise sequestered CO2 gases, from the burning of fossil fuels, the water vapor only amplifies it’s effects.

In a pre-industrial climate system, naturally occurring CO2 would of course make it into the atmosphere and work along side water vapor to regulate global temperatures. Geologically speaking, however, climate shifts normally happen on a scale of thousands of years, not hundreds, like we are observing now. The rate at which we are releasing carbon dioxide into the atmosphere is so fast that geologic processes cannot remove it fast enough, therefore leaving an excessive amount of CO2 in the atmosphere that is now being amplified by the already present water vapor. This process feeds a positive feedback loop of warming that could quite possibly be irreversible.

The next time you are confronted with an article claiming that volcanoes are emitting more CO2 than human activity, remember the real science. Remember that scientists are going through great lengths to understand climate change so that we can either find a solution, or adapt to changing environments.


Click here to learn more about green house gases (GHG’s) and how they affect our climate.


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USGS, 2016, volcanic gases can be harmful to health, vegetation and infrastructure, https://volcanoes.usgs.gov/vhp/gas.html: (accessed, January, 2017)

USGS, 2007, Which produces more CO2, volcanic or human activity?https://hvo.wr.usgs.gov/volcanowatch/archive/2007/07_02_15.html: (accessed, January, 2017)

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