Volcanic vs. Human-Caused CO2 Emissions - Updated Graphic

I create illustrations for authors of Skeptical Science posts, but lately I've had a hiatus of this activity. Some may even call it a pause, or a trend reversal. Others, however, know that there never was a pause, that the time I would have spent illustrating posts was absorbed in the deep ocean of our contribution to Denial101x. I'll be releasing some of these sequestered illustrations in our climate graphics section.

The first is a rework of our volcanic vs. human-caused emissions sketch, which appeared in "Message from the Past" by SKS author Peter Jacobs (See Denial101x Our comparison of volcanic to anthropogenic emissions summarized Gerlach 2011 (see EOS 14 June 2011), which estimated the ratio of human emissions to volcanic at 130 to 1. Though the clouds in my drawing were metaphors, I aimed for eye-ball accuracy by drawing 131 boxes:

Let me count the squares

SKS author and geologist Andy Skuce also discussed volcanic emissions in "The CO2 Rise Is Man Made" (see DENIAL101x Andy estimated a range from 60–120 to 1 for anthropogenic to volcanic emissions. The lower estimate (120 vs 130) is based on research by Burton, Sawyer and Granieri 2013 that estimates volcanic emissions to be higher than does Gerlach 2011, and the range (60-120) is based on whether one counts only total outgassing (60:1) or net outgassing (120:1). Consider for comparison, if a car sucked back in one half of its emissions, the net emissions from the car would be 1/2 the total. Likewise, if the production of volcanic rocks releases CO2 and then reabsorbs half of it, then the net emissions from this source is 1/2 of the total emissions.

Using net emissions, the new diagram illustrates a 100:1 ratio of human related emissions to volcanic along with the older estimate:

The 100:1 ratio understates the quantity of human emissions. It's a conservative estimate that assumes there are undiscovered natural sources. For example, much of the ocean floor is not explored, so additional sources may be found; however, as Andy explains in "The CO2 Rise is Man Made," ocean sources tend to be low emitters, so additional discoveries are not like to exonerate our fossil-fuel use.

Why not discount human emissions too? Since the biosphere and oceans absorb roughly half of our emissions, why not say the human to volcanic ratio is 50:1? Mainly because humans do not create sinks when we burn fossil fuels or manufacture cement; rather we are consuming the storage capacity of natural sinks. An exception may be emissions from land clearing for agriculture, but this is small compared to fossil fuel use.

We should be mindful that we do not know whether the storage of anthropogenic emissions in the biosphere and oceans is stable. What we put into the biosphere and ocean could be released back into the atmosphere, as when forests burn or when ocean currents warm and shift.

It is tempting to watch a volcano erupt, see it's plume in pictures taken from orbit, and think what humans are releasing is insignificant. But a long term look at the rate of volcanic to anthropogenic emissions shows that we are responsible for most of the rise of CO2. Hopefully, responsibility for our emissions will soon translate into control over them.

Posted by jg on Tuesday, 8 September, 2015

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