Where is All That Carbon?

A Summary of Earth's Carbon Stocks

The text below was written by a scientist who belongs to the species we call “naked apes” and who call themselves “humans.” They seem to be able to understand the main elements that control the ecosystem of their planet, but, at the same time, they are unable to act on them to maximize the functioning of the biosphere that keeps them alive. They operate, instead, on the principle of maximizing a curious dimensionless entity that they call “money.” As long as they remain at this stage, I am afraid that they will face extinction in the near future. It is sad, because they are a clever species, and they could have contributed to the galactic civilization. But the galaxy is big, and the Reptilian Federation will continue ruling it wisely and justly.

Mera Te’ Ai enge’ite, chief scientific officer of the Reptilian starfleet

Guest post by Ugo Bardi

All the carbon atoms inside every living being on Earth have been cycled innumerable times in and out of the many molecular forms that carbon can take. Carbon forms the polymers that create living beings. It is stored in oceans as carbonate ions, in the ice as methane, in the geosphere as solid carbonates and “recalcitrant” polymers, and in the atmosphere as carbon dioxide.

Here is an image showing the distribution of carbon in the ecosphere's different reservoirs. The data are carbon mass in Gigatons (source).

There is a further stock, which is the sediment layer, where carbon is mostly in the form of kerogen. It is of the order of a million gigatons but, fortunately, it is not mobile; that is, it does not exchange carbon with the ecosphere. It is from Kerogen that fossil fuels are derived by natural processes. Kerogen is also the place where most of the carbon that formed the current oxygen mass in the atmosphere is stored, some 1,2x10^6 gigatons. Take into account that in the photosynthesis reaction, one molecule of CO2 creates (indirectly) one molecule of Oxygen (O2) and one carbon atom (C). But one carbon atom weighs ca.1/3 of a molecule of oxygen, so in terms of the number of molecules/atoms, there is much less oxygen than you would expect if all the Oxygen had remained in molecular form. But that’s because oxygen reacted with other compounds, e.g. iron, and was turned into solid compounds.

You can understand the intricate network of exchanges from this figure (source). The data are in “Petagrams” (Pg), which is the same as Gigatons (Gt). The arrows are connected to red numbers in Pg/year. (the “yr-1” is sometimes missing). The red number is sometimes in Pg and sometimes in Pg/year, but it always represents the perturbation caused by human activity.

Note that some reservoirs exchange carbon relatively slowly compared to their size. However, they are all dynamically linked. The main linking element is atmospheric carbon dioxide (CO2), which exchanges carbon with practically all the other reservoirs, in some cases directly and in others indirectly.

Now, some interesting takeaways from these data

1. The mass of carbon in the atmosphere and in the biosphere used to be approximately the same before the industrial age. Now, the atmosphere contains much more carbon.

2. Over a couple of centuries, humans increased the quantity of carbon in the atmosphere of about 50%; a total of 260 Gt. This is about half of the total amount of carbon stocked in the land biosphere. If we wanted to offset this amount by increasing the mass of the biosphere, we should increase it of about the same amount, that is 50%. Planting trees is simply futile in terms of “offsetting” the carbon unbalance. At least as long as we keep pumping 10 gigatons of carbon into the atmosphere.

3. We could burn the whole biosphere, and that would ca. double the amount of carbon in the atmosphere in comparison with the pre-industrial amount. But it would hardly make a dent in the oxygen concentration in the atmosphere. It seems that we are engaged in doing exactly that, turning the planet surface into a concrete slab.

4. Soils could be a much better place where to store the excess carbon, since we would “just” need to increase the carbon content of about 10% to rebalance the atmosphere. Agriculture and grasslands do store plenty of carbon in the soil, but we don’t know if it could be done fast enough.

5. The deep ocean seems like an even better place to store excess carbon, assuming that the carbon stored there in the form of carbonate ions is stable and that we find a way to push carbon dioxide down there.

6. Perhaps the best idea to get rid of some carbon from the atmosphere would be to increase the global fecal pellet carbon flux to the bottom of the ocean which, at present, could be in the range of 5 to 10 Pg C/year. That would mean revitalizing the ocean’s ecosystem by stopping overfishing. (irony on) Which is obviously impossible because it would negatively impact economic growth (irony off).

Acknowledgment: the author thanks the Reptilian Starfleet Headquarters for hosting his considerations on their blog