As a matter of fact, no one knows whether this meme graphic is correct or not. The specific eruption was not named or dated, and, in any event, humans have been around for only a few of Etna’s major eruptions during its past 500,000 years or more of eruptions.
A frequent response to this graphic meme is another meme popular among global warming proponents but one which is easily refuted:
“The projected 2010 anthropogenic CO2 emission rate of 35 gigatons per year is 135 times greater than the 0.26-gigaton- per-year preferred estimate for volcanoes.”
Gerlach’s meme quoted immediately above (i.e. Gerlach’s calculation based on a very small set of volcanoes) has been been thoroughly debunked in the scientific literature. But, for the sake of argument, let me illustrate the futility of his and AGW’s argument.
Let’s assume that Gerlach’s calculation is correct and other literature references are correct that claim that Etna produces 10% of the total annual CO2 emitted from volcanoes. Then, just for purposes of this illustration, Etna produces 0.026 gigatons CO2 per year (i.e. 10% of the total volcanic CO2 annual emissions) and humans produce 35 gigatons per year. Mt Etna has been producing this amount of CO2 for about 500,000 years, not including any major Etna eruptions, based on Etna’s passive emissions as measured today. Using Gerlach’s calculation, humans produce 35 gigatons of CO2 per year, and let’s says humans have been doing that since the beginning of the industrial revolution, i.e. for 200 years, which is a huge over-estimation.
In summary, for this quick estimate, humans have produced 7,000 gigatons of CO2 and Mt Etna has produced 13,000 gigatons of CO2. But, Mt Etna is only one of thousands of CO2-emitting volcanoes and there are many other rifts and tectonic boundaries which have been pumping gigatons of CO2 into the oceans and atmosphere for thousands of years before humans (as far as we know) existed. The meme in the Mt Etna graphic is making a valid point: human CO2 is insignificant with regard to the climate of this planet.
For more detail and background, see: http://carbon-budget.geologist-1011.net/