Can volcanos change the climate?

Question

I have heard politicians claiming that volcanoes are the sole cause of global warming and using so called "NASA data" to show that the Earth is actually cooling instead of warming.

While the nature of this site is for specific questions and not for political debate, we all know from the Year Without a Summer that volcanic gases can impact the weather severely making it very cold or hot.

My question is this:

Can a volcanic eruption, either a single or multiple explosions, be the sole cause of global warming at the planetary scale? Can volcanoes really change the climate so fast, relative to the geological timescale, that they produce the abnormal levels that we see today?

I'm aware of the year without summer, but that ended in a nanosecond, geologically speaking.

Answer 1

Can volcanos really change the climate so relatively (geological timescale speaking) fast, up to the abnormal levels that we are seeing today?

Even more so.

You wrote about the 1815 eruption of Mount Tambora. While that was an extremely large eruption in terms of written human history, it was rather tiny compared to the absolutely colossal volcanic events whose histories have been written in the rocks. Multiply the Tambora eruption by a factor of 10000 or more and you'll get things like the Deccan Traps and Siberian Traps.

A number of geologists think that it was the formation of the Deccan Traps rather than the Chicxulub impact event that killed the dinosaurs. A much larger fraction think the combination of the two dealt a one-two punch that ended the reign of the dinosaurs.

The Siberian Traps are still deemed by many, if not most, geologist as the leading contender for the cause of the Permian–Triassic extinction event. This was by far the most severe extinction event ever, much greater in impact than the Cretaceous–Tertiary extinction event that killed the dinosaurs. The lava released by the Siberian Traps covered an area the size of Europe (or larger, depending on who you read). It may have triggered massive fires in coal deposits, significantly adding to the greenhouse gases.

That said, what's happening to the Earth's atmosphere now is not a result of volcanic activity. It's us. (That of course is assuming that the massive amounts of hot air that comes out of the mouths of politicians is not classified as volcanic.)

Answer 2

That the CO₂ imbalance causing global warming is anthropogenic is accepted by 97% (source) of climatologists. This site has this to say about human's effect on CO₂ imbalance:

But consider what happens when more CO₂ is released from outside of the natural carbon cycle – by burning fossil fuels. Although our output of 29 gigatons of CO₂ is tiny compared to the 750 gigatons moving through the carbon cycle each year, it adds up because the land and ocean cannot absorb all of the extra CO₂. About 40% of this additional CO₂ is absorbed. The rest remains in the atmosphere, and as a consequence, atmospheric CO₂ is at its highest level in 15 to 20 million years (Tripati 2009). (A natural change of 100ppm normally takes 5,000 to 20,000 years. The recent increase of 100ppm has taken just 120 years).

Human CO₂ emissions upset the natural balance of the carbon cycle. Man-made CO₂ in the atmosphere has increased by a third since the pre-industrial era, creating an artificial forcing of global temperatures which is warming the planet. While fossil-fuel derived CO₂ is a very small component of the global carbon cycle, the extra CO₂ is cumulative because the natural carbon exchange cannot absorb all the additional CO₂.

Also, this site lists the acceptance of anthropogenic global warming from eighteen different scientific associations.

I'm not sure politicians are the final authority for global warming.

Edit: it has come to my attention that I did not actually answer the question posed in the title of this question, to wit: "Can volcanos change the climate?" I'll have to admit I did not. Taking the title and the body together as one topic I'll try to address the contribution volcanoes make to global warming.

This site has this to say about the contribution of CO₂ from volcanoes:

Volcanic eruptions can enhance global warming by adding CO₂ to the atmosphere. However, a far greater amount of CO₂ is contributed to the atmosphere by human activities each year than by volcanic eruptions. T.M.Gerlach (1991, American Geophysical Union) notes that human-made CO₂ exceeds the estimated global release of CO₂ from volcanoes by at least 150 times. The small amount of global warming caused by eruption-generated greenhouse gases is offset by the far greater amount of global cooling caused by eruption-generated particles in the stratosphere (the haze effect).

And this one has this:

Gas studies at volcanoes worldwide have helped volcanologists tally up a global volcanic CO₂ budget in the same way that nations around the globe have cooperated to determine how much CO2 is released by human activity through the burning of fossil fuels. Our studies show that globally, volcanoes on land and under the sea release a total of about 200 million tonnes of CO₂ annually.

This seems like a huge amount of CO₂ , but a visit to the U.S. Department of Energy's Carbon Dioxide Information Analysis Center (CDIAC) website (http://cdiac.ornl.gov/) helps anyone armed with a handheld calculator and a high school chemistry text put the volcanic CO2 tally into perspective. Because while 200 million tonnes of CO2 is large, the global fossil fuel CO₂ emissions for 2003 tipped the scales at 26.8 billion tonnes. Thus, not only does volcanic CO₂ not dwarf that of human activity, it actually comprises less than 1 percent of that value.

Certainly volcanoes can cause short-term climate effects. Pinatubo in 1992 reduced global temperatures by 0.5 to 0.6 degrees Celsius (source). IOW, it lowered temperatures, not raised them. So I think it's safe to say that humans contribute considerably more to warming than do volcanoes.

Answer 3

Can volcanos change the climate?

Yes, but it has to be a very big one, like once every 100,000 years, perhaps every million years. The volcanic eruption of 75,000 years ago may have kickstarted, or assisted the onset of the last ice age, though debates on that remain unresolved. It may have also threatened the survival of the human race and caused extensive ecological disasters.

See Toba Catastrophy Theory.

I have heard politicians claiming that volcanoes are the sole cause of global warming and using so called "NASA data" to show that the Earth is actually cooling instead of warming.

All of this is wrong on so many levels. Volcanoes are a very small contributor of CO2 and they make it colder on average, not warmer.

While the nature of this site is for specific questions and not for political debate, we all know from the Year Without a Summer that volcanic gases can impact the weather severely making it very cold or hot.

Most volcanic eruptions have very little effect.

Mt. Pinatubo in 1991 is thought to have cooled the planet for a couple of years, by maybe 1/2 of 1 degree, if that. Mt. Tambora in 1815 was much larger and had a more drastic cooling effect, but only for a few years and only one year was the year without summer. The reason for this is the cooling volcanic gas and particulates, primarily SO2, has a very short half life in the atmosphere. By some estimates, it's half life is as short as a few days, though for larger amounts, because it primarily rains out of the atmosphere, the half life might be longer for big eruptions.

Source and Source. (best sources I could find with a quick google search).

It's an interesting question as to why Volcanoes are as good at cooling the earth as they are, given that SO2 has a half life of just days, but the answer to this is at least in part, that only very large volcanoes measurably cool the planet, and it might not take that much SO2 to reflect enough sunlight to cool the earth, at least for a month or two, which might be enough to cause a measured drop in temperature for the year, and in extreme cases, a year without summer.

But the short answer is that Volcanoes don't heat the Earth, they cool it, and they're not particularly good at cooling it either. Their effect is usually quite temporary. If a Volcano is strong enough to stop man made climate change in it's tracks, it would probably also cover half a continent with ash and significantly hurt our food supply for the year and perhaps, remove most of the ozone layer for a time. The temperature effects would be the least of our problems. (Hopefully, an eruption like that won't happen for several tens of thousands of years, perhaps a few hundred thousand years, but, a gonzo eruption will happen again at some point, probably not in our lifetime though.

My question is this:

Can a volcanic eruption, either a single or multiple explosions, be the sole cause of global warming at the planetary scale? Can volcanoes really change the climate so fast, relative to the geological timescale, that they produce the abnormal levels that we see today?

Volcanoes are primarily agents of cooling not warming, so one might be able to trigger an ice age, though warm northern hemisphere summers and the current CO2 levels are unlikely to let an ice age actually take hold, so that's a long shot and it would need to be a huge eruption.

It's far more rare for volcanoes to cause warming. What can happen, if the volcano is large enough is that it could kill much of the plant life on earth and decomposition could lead to an increase in Greenhouse gas, but that would probably be temporary as plant life tends to grow fairly quickly and volcanic ash is actually fairly fertile. Another way is if the volcano sets fire to a large bed of coal, which is thought to have been the case with the Siberian traps, mentioned by David Hammen, thought to be the largest extinction in the history of the Earth.

The cooling effect of SO2 and particulates that reflect sunlight away from the earth is short lived. CO2, in large enough amounts is much longer lasting in the atmosphere, 100 years half life or longer, especially if the oceans start warming and releasing some of their stored CO2, so the burning of an entire bed of coal over half a continent may have added enough CO2 to the air, that once the SO2 and Particulate driven cooling was over, the Earth could have warmed measurably, so, it is possible for a Volcano to cause global warming, but it has to be positioned under a large coal deposit and enormously big. It's very rare, to say the least.

Generally speaking, anyone who says Volcanoes can cause global warming is either lying or ignorant, but if a volcano is an extinction level event, hundreds of times larger than the one that caused the year without summer, which happens every, Oh, I don't know, once every million to several million years, then such a volcano might trigger global warming, but if that happens, the warming will be years away and very far from our biggest concern.

(too long?)