Do Volcanoes Cause Global Warming?

Today's Guest Blogger, Lisa Moore, is a scientist in the Climate and Air Program.

The fiery centers of volcanoes burn carbon-containing rocks from deep within the earth, and thus emit the greenhouse gas carbon dioxide (CO2). There are a fair number of volcanoes in this world, all emitting CO2, so couldn't this be the cause of global warming?

In a word, no. Here's how scientists know that climate change is not from volcanic activity.

On average, volcanoes spew over 130 million tons of CO2 into the atmosphere each year. That sounds like a lot, but compare it to global fossil fuel emissions: in 2005, we emitted more than 27 billion tons of CO2. Emissions from human activity are more than 200 times the emissions from volcanic activity.

Those numbers are direct measurements from scientists reported on U.S. government sites, so I could stop here. But for those who still are skeptical, I'll demonstrate it another way as well.

If the increase in CO2 came from volcanoes, we would expect to see abrupt increases in CO2 after large eruptions, but we don't! The figure below shows monthly mean CO2 levels since 1958, measured at the Mauna Loa observatory in Hawaii.

As you can see, CO2 is steadily increasing. The arrows show the five largest volcanic eruptions during that time period. They didn't leave much of a mark, did they?

We can see evidence of volcanic eruptions in another dataset: temperatures. But the effect of eruptions is to cool the globe, rather than heat it!

Huge volcanic eruptions can shoot significant amounts of sulfur dioxide into the stratosphere. This gas is converted to sulfate aerosols, which reflect sunlight and have a cooling effect. Because of the way the atmosphere circulates, tropical volcanoes have a stronger cooling effect than mid- and high-latitude eruptions of the same magnitude.

The graph below is Figure 1 in Chapter 8 [PDF] of the latest IPCC report. The black line shows temperatures, the yellow lines show results from 14 different models, and the red line is the average of all the simulations. As you can see, the four biggest tropical eruptions over the past century had slight cooling effects.

The Mount Pinatubo eruption was especially interesting because it provided a great early test for climate models. After Pinatubo exploded, scientists entered emission measurements into their climate models and compared the results with actual observations. The next figure shows that comparison (a larger version is available here). The solid line shows temperature measurements and the dashed lines show model simulations.

Two things really jump out of this graph. First, the reflective aerosols from the eruption had a substantial cooling effect. And second, the climate model did a pretty darn good job of predicting the resulting climate change.

One more point worth noting: this particular model experiment was published 10 years ago. Scientists haven't stopped testing or improving their models since then, so today's models are even more accurate.

Speaking of models… that is a big topic!  Maybe Bill should do a series about climate modeling – what do you think?

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4 Comments

  1. K.C. Weber
    Posted May 21, 2007 at 8:37 pm | Permalink

    Many consider Earth to be a fragile planet, and to take care of it needs to be like walking on eggs. Yet, the formation of all the planets was violent and explosive. During the early times of the solar system, as the planets formed, there were massive collisions between planets, asteroids, and meteors. Arizona’s Meteor Crater is an impact crater on the Earth that is 4,000 feet wide and 600 feet deep made from an asteroid 150 feet across. In the early stages of the Earth’s formation, volcano’s also filled the Earth’s atmosphere with a nearly continuous flow of pollutants of ash and gasses. The Earth was not a very hospitable place for life during the early formation periods, and if we used today’s reasoning, it would be concluded that life should never have formed on the Earth.

    Yet, even though the Earth has been hit bay many large comets, asteroids, and meteors, only a few impact craters can be seen today, such as Arizona’s Meteor Crater. Most of the others are difficult to find because of natural erosion and the fact that they are now overgrown with plant and animal life again. Also, even though the Earth’s early atmosphere was filled with pollutants that once caused a global warming that we would consider disastrous today today, the Earth’s air and water go through a continuous cleansing process and eventually becomes clean again. Over long periods of time, the effects of pollution always get dispersed and disappear into the ecological system.

    For those who think that man’s influence on the Earth is so permanent and damaging, you will be surprised to know that if man were somehow killed off and stopped influencing the Earth altogether, all traces of man would eventually be absorbed back into the ecological system and disappear, just as many ancient civilizations have disappeared in the past.

    Sincerely,
    K.C. Weber

  2. Brian
    Posted May 22, 2007 at 2:45 pm | Permalink

    The crisis in global warming and climate change may well turn out to be a human one moreso than a planetary one. There is little doubt that Earth would find equilibrium once again if climate changes were severe enough to wipe out the human species.

    As K.C. Weber mentions this planet has recovered from catastrophes in the past and will do so again. If we humans manage to eliminate ourselves (or even reduce our numbers), we will eventually cut our emissions to the point where natural processes will begin to reverse our efforts to poison the planet.

    The problem is the "long periods of time" required to do this are very different in geologic terms versus human ones. We don't have millennia to let nature run its course. We have to act now if we want to have a positive impact on the human condition for future generations.

  3. K.C. Weber
    Posted May 23, 2007 at 2:49 pm | Permalink

    I agree wholeheartedly with Brian. When we pollute, we are the ones who suffer, along with other life around us. The Earth and it's enviornment will eventually rebound and return to normal, as I stated above. But in the meantime it is mankind and other forms of life who will be hurt. We are hurting ourselves and other forms of life much more than we are hurting the Earth it's environment.

  4. selsbecker
    Posted February 4, 2009 at 4:11 pm | Permalink

    I agree with both Brian and Webster about the fact that we are hurting ourselves and others rather than the planet however global warming is questionable itself. For the past 50 years or so climatologists and scientists have been studying the earth's atmosphere and so and and so forth. But if you can remember about 30 years or so ago the scientiests of that time were warning us of another ice age, that the world was going through a cooling period. We were all going to freeze to death. Well here we are in 2009 and now we are talking about a global warming period. It doesn't matter how much proof that you can gather from how much emmisions are let out each year or even that there is a hole in the ozone, you can't simply say that global warming is happing by how much CO2 is put into the air each year based on a 30 or 50 year scale…the earth has been around for a LONG time and you would have make tests and experiments over centuries and even thousands of years to determine this…which we can't. The earth will flush itself out just like it always has…i'm not saying that we shouldn't take better care of our planet and ourselves as well as others…just that just because it seems like it is happening doesn't mean that it really is.

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