And if ultimately, the responsible for global warming were volcanoes more than humans? This is what a climatosceptic post, relayed on Facebook, wrongly claims. Accompanied by an image of Mount Etna erupting, the post states, in English that “this little burp [l’éruption] Mount Etna has already released more than 10,000 times more CO2 into the atmosphere than humanity has since being on Earth, but don’t worry, a scam is in the works to tax your tiny footprint [carbone]. »
The post does not give any date for this eruption, nor any figures for the quantities of CO2 which would have been released by the volcano.
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Scientists interviewed by 20 minutes are unanimous: this comparison is false. “It’s completely delusional,” says Edouard Kaminski, researcher in physical volcanology at the Institute of Earth Physics in Paris. And the scientist to do the calculations: “For an “intense” degassing of Etna, measurements in 2015 gave 10,000 tonnes of carbon injected into the atmosphere each day. In the 2000s, IPCC estimates for fossil fuels and cement works were around 20 million tonnes of carbon per day. If Etna formed a powerful plume throughout the year – which is of course not the case – it would therefore not represent more than 0.05% of the injections due to fossil fuels and cement works, not counting the other anthropogenic sources of CO2 like deforestation. »
The CO2 emissions of this volcano are therefore absolutely not comparable to the volumes resulting from human activity.
“It would be known if the volcanoes emitted more gases than our greenhouse gases, we would not be talking about the problem for the climate”, abounds Cathy Clerbaux, director of research at the CNRS. Where does the claim in this misleading post come from? No source is named there, but for the scientist the confusion could come from the fact “that there is an enormous amount of carbon which is stored below from the surface of the earth, in the mantle, in the crust, in the core”. But that doesn’t mean that these gases “are going to be spewed out by the volcanoes!” “.
In the past, eruptions have temporarily changed the climate, but “they had a negative impact: instead of warming, it tended to cool”, adds Cathy Clerbaux. “The net effect of any large eruption relevant to our human timescale is always a cooling effect,” also recalls Yves Moussalam, a researcher at New York’s Columbia University. This effect is “mainly due to the emission of sulfur and the formation of sulphate aerosols in the stratosphere which reflect sunlight, thereby cooling the surface”.
In 1991, the eruption of Pinatubo, in the Philippines, generated “a global cooling estimated at 0.6°C over a period of fifteen months”, recalls the researcher. If we go back in time, in 1815, the eruption of Tambora, in Indonesia, “caused the famous” year without summer “”.
As for those who would be inclined to wish such a volcanic eruption to occur in our warming context, they are on the wrong track, warns Yves Moussalam: “A volcanic eruption the size of Tambora or worse is absolutely not something to hope for in the fight against the current warming. Global cooling after such an eruption would be brutal and catastrophic for agriculture worldwide. »