I was watching a science/myth Youtube channel (science mixed with a lot of speculative/fantasy content) with 2M+ followers and the Youtuber said volcano made emissions were higher than human made emissions. Now, I thought this was wrong and apparently some figures I saw in articles showed this was wrong, but then, I found this article

Skeptical - Human CO2 smaller than natural emissions

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.

So this article seems to be stating than in general natural emissions (not only volcano emissions) are indeed higher than human made emissions but human made emission are really bad anyway because they can't be absorbed and break the natural balance.

So now I really don't know if they are higher or lower. Then my question is , which percentage of CO2 emissions are human made emissions? and how volcano only natural emissions compare with human made emissions?

  • $\begingroup$ I'm going to point you to this Forbes article that puts yearly volcanic CO2 emissions at 645 million tons per year versus 29 billion tons from himan activity. $\endgroup$
    – Spencer
    Commented Feb 7, 2019 at 13:04
  • $\begingroup$ You've got two separate questions here: 1) The easily answered volcanic vs human fossil fuel CO2 emission; and 2) The not so easily answered amount of carbon involved in the carbon cycle. You can get an idea by looking at annual variation in the Keeling Curve ttps://en.wikipedia.org/wiki/Keeling_Curve which basically represents the difference in summer/winter activity of plants in the northern hemisphere temperate zone. (Because there's much more land area in the north than the south.) $\endgroup$
    – jamesqf
    Commented Feb 7, 2019 at 18:20

1 Answer 1


First of all, the amount of carbon cycling trough the Earth's system is irrelevant to the discussion of the changes in atmospheric $\text{CO}_2$ concentration or ocean acidification. In the same way that the volume of water cycled by the filtering system of a swimming pool is irrelevant to the level of the pool. What matters are the net inputs and outputs of water.

Let's look at this diagram of the Earth's carbon storage and fluxes through the carbon cycle.

enter image description here

Figure by Dave Bice at Carleton College.

The total amount of carbon is indeed huge, and the total fluxes add up to almost 700 Gigatons of carbon per year. Note that only ~400 Gt are transferred as $\text{CO}_2$, the rest is organic matter.

The number in the diagram are not precise, but they are very good approximations. The figure given in the diagram for humans burning fossil fules is 6 Gt of carbon, that corresponds to 22 Gt of $\text{CO}_2$, which added to other human made emissions probably add up to something similar to the 29 Gt of the reference you cited.

The amount of $\text{CO}_2$ released by volcanic activity varies widely in time, but the amount given in the figure is an average value, and amounts to 0.6 Gt of Carbon, equivalent to 2.2 Gt of $\text{CO}_2$. But pretty much the same amount is removed by subduction. Therefore, volcanic activity is not a significant LONG TERM source of $\text{CO}_2$. And by long term I mean millions of years.

So you can argue that natural emissions are larger than human emissions. Sure. The respiration of plants and animals produce 8 times more $\text{CO}_2$ than humans, but plants take it back through photosynthesis.

Atmospheric $\text{CO}_2$ have varied widely through Earth's history, but in the last several thousands years it have been pretty stable, because all the sources were in balance with the sinks, leading to a very small net change in $\text{CO}_2$ concentration in the atmosphere and oceans (there in the form of carbonic acid).

However, this balance was disrupted by the industrial revolution and human emissions, mostly due to the use of fossil fuels.

Going back to the swimming pool analogy: evaporation might be tiny compared with the volume of water turned around by the filtering system, but give it long enough time and your swimming pool will be dry.

We added a source of carbon in the carbon cycle, and if we don't remove it or add an equivalent sink (carbon sequestration), the concentration of $\text{CO}_2$ in the atmosphere and carbonic acid in the oceans will keep rising.

Returning to your question, using the figures in the diagram, human emissions would account for ~3% of total emissions. But that doesn't matter at all. The point is that human emissions are the ones upsetting a system that was in balance, and are triggering an increase in atmospheric $\text{CO}_2$ concentrations and consequent ocean acidification.

  • $\begingroup$ Adding the numbers in the black arrows which reachs the atmosphere it adds up to 200. How do I reach to the 400 you mentioned? $\endgroup$
    – Pablo
    Commented Feb 8, 2019 at 14:39
  • $\begingroup$ @Pablo (110+50+59.4+90+90) I refereed ti fluxes going in and out. To calculate the final ~3%, I counted only emissions that are 206 Gt $\endgroup$ Commented Feb 8, 2019 at 14:55
  • $\begingroup$ Re "The respiration of plants", did you mean "The respiration of animals"? (Or course plants do respire too...) $\endgroup$
    – jamesqf
    Commented Feb 8, 2019 at 17:49
  • $\begingroup$ @jamesqf I meant respiration of plants. Although I don't know how much of those 50Gt of carbon due to respiration correspond to plants and animals, but I asume plants have the biggest share as their biomass is so much bigger, but I might be wrong. $\endgroup$ Commented Feb 8, 2019 at 18:26
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    $\begingroup$ I've seen estimates of human respiration equivalent to 1-10% of the 10 GtC annual anthro emissions, so say about 1 GtC for all animals. That's lost in the errors on plant and soil respiration. Note that the below ground contribution from plants (from roots, etc) is included in the soil respiration component. $\endgroup$
    – Deditos
    Commented Feb 10, 2019 at 15:38

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