Natural Carbon Balance

The total Biomass on Earth is 560 billion tonnes of carbon [see ref] most of which is in the form of plant life. If we now calculate the mass of carbon atoms held in the atmosphere in the form of CO2 for a concentration of 280 ppm then we find there is  600 billion tonnes  [see ref using 280 ppm] . These two are almost identical which in my opinion cannot be a coincidence. It seems that nature balances the CO2 levels in the atmosphere so as to match the carbon content  in the Biosphere (and vice versa). During Ice Ages the spread of ice sheets reduces the available land biosphere and as a  consequent CO2 levels fall. These then recover during an interglacial. Over the very long term plate tectonics ensures that any buried carbon by rock weathering is recycled through volcanoes.

Now of course in the short term humans have cleared large areas of forests and added CO2 to the atmosphere, so the two carbon sinks were even closer 100 years ago. I suspect that  what this all means is  that the living biomass carbon content is slowly being returned to the atmosphere at the same rate as  photosynthesis is consuming carbon from CO2 and  sustaining oxygen levels in the atmosphere. Photosynthesis by plants liberates oxygen to the atmosphere as a by-product. Animals then consume both oxygen and biomass to live, thereby returning their “waste” CO2 back to the atmosphere maintaining a balanced  level of 21% of the atmosphere. I suspect it is probably forest fires that currently limit the oxygen content to ~21% of the atmosphere.

During the early Carboniferous period the continents were joined together in one large continent  (Pangea) and the climate was much warmer and humid with CO2 levels reaching 1500 ppm and higher levels of oxygen than today. Therefore if we assume the same relationship holds, then there must have been about four times more biomass compared today in order to “balance” the 1500 ppm in the atmosphere. During the Carboniferous period the world’s coal reserves were buried in inland swamps. This  carbon loss from the biosphere therefore led to a gradual reduction of atmospheric CO2,  eventually leading towards current levels and a cooler dryer climate ending coal deposits.

Currently atmospheric CO2 levels are out of balance with the earth’s biomass. This is firstly because we have burned some of the buried Carboniferous carbon (coal) and secondly because we have also curtailed the natural biomass to meet our farming needs.  The carbon deficit seems therefore to be as follows.

  1. Biomass has fallen from 600 billion tonnes to 560 billion tonnes  ( A deficit of 40 billion tonnes )
  2. The carbon content of atmospheric CO2 has risen from 600 billion tonnes (280ppm) to 900 billion tonnes (417ppm)  (A surplus of 300 billion tonnes )

Reforestation would probably be the quickest route to begin rebalancing carbon. Burning biomass as a renewable energy source looks like a bad idea as it goes in the opposite direction. Much of Africa also still relies on wood  and charcoal for cooking.

Eliminating the burning of fossil fuels means finding an alternative energy source. The problem with most traditional renewable energy sources is that they are weather dependent and are often out of phase with energy demand. It is mainly  Hydro , Geothermal and Tidal power that are reliable and predictable sources. Furthermore if we want to electrify transport and heating then demand will more than double. That means eventually reaching a grid capacity of ~ 80 GW.

Only Nuclear power can realistically achieve this goal, perhaps eventually through Nuclear Fusion. We then hopefully will be able to rebalance global carbon.

About Clive Best

PhD High Energy Physics Worked at CERN, Rutherford Lab, JET, JRC, OSVision
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27 Responses to Natural Carbon Balance

  1. Nick Stokes says:

    “These two are almost identical which cannot be a coincidence. It seems that nature balances the CO2 levels in the atmosphere to match that in the Biosphere. “
    It is a coincidence. You have given no argument to the contrary. Those numbers are not levels, but amounts. Physical systems can respond to concentrations, but not amounts. Nature has no way of working out what is the global total. That is our calculation.

    “Reforestation would probably be the quickest route to begin rebalancing carbon.”
    Only if the trees will grow. Vegetation is mainly limited by sunlight and water availability. It’s true that we should be able to returned cleared land to forest, if forest it was before. But if there wasn’t forest on that land before, then there is probably a reason.

    • Clive Best says:

      OK so let’s check if it works.

      1. If you could remove all CO2 from the atmosphere then all plant life would die. So the zero point is certainly true.

      2. Coal reserves left in 2016 were roughly 1.2 billion tonnes and CO2 levels were 400 ppm. Adding 1.2 billion tonnes to the atmosphere increases CO2 levels by about twice the current value. So that takes it up to over 1200 ppm. That is not far off CO2 levels in the Carboniferous period.

      • Anteros says:

        I’m guessing your billions have 12 noughts?

      • Andrew Carey says:

        Could you show your working for the above please Clive. You say that there were roughly 1.2bn tonnes Coal as declared reserves. Based on https://en.wikipedia.org/wiki/List_of_countries_by_coal_reserves there were 250bn tonnes of Coal reserves in the USA alone. And we haven’t even begun on Coal resources which has a different definition – the harder to get stuff which is known to be there but not extractable economically so not classed as a reserve for the purpose of commodities markets.

        • Clive Best says:

          Yes you are quite right. I got it wrong and global coal reserves are more like 1.0 trillion tonnes !
          However the CO2 estimates are in the right ball park. If we suddenly burned all the coal we would add 1000 billion tons of carbon to the current atmosphere of 600 billion tonnes, giving a total carbon content of 1600 billion tonnes. This would lead to a CO2 peak concentration of ~1500 ppm

  2. Clive Best says:

    Photosynthesis : 6CO2 + 6H2O = C6H12O6 + 6O2

    For every 6 CO2 molecules absorbed 6 O2 molecules are produced.

    Aerobic respiration takes place in mitochondria : C6H12O6 + 6O2 = 6CO2 + 6H2O

    Photosynthesis and cellular respiration are both part of a mutually beneficial relationship. Cellular respiration cannot occur without photosynthesis, and photosynthesis cannot occur without the help of its partner.

  3. Cytokinin says:

    Interesting thoughts Clive. There seems to be some evidence that plant biomass is increasing to balance the CO2 levels but moving towards equilibrium is a long slow process.

    My memory is that the Carboniferous period was ended by fungi that developed the ability to munch lignin. No more fossilized lignin, no more lignite.

  4. Randall Hislop BSc MSc BEd says:

    Excellent article. Reforestation should involve the re establishment of all underbrush. Underbrush is a huge biomass and extremely useful for preventing fires and floods if it has water absorbing vegetation that keeps the ground moist during droughts and absorb water during floods. The elimination of trails for people to travel on in low lying areas would be necessary and have many benefits in the terms of developing biomass. Main roads are necessary for transportation, but ditches could be filled with water absorbing underbrush species that would soften the impact of vehicles that leave the road preventing fatalities.

  5. Andrew Carey says:

    There are sources quoting this: “”The total mass of the atmosphere is approximately 5.1480×10 18 kg”
    Multiply that by 417 and divide by a million gives approximately 2147 billion tonnes of atmospheric Carbon Dioxide. I’m leaving out methane and other carbon compounds.
    I notice you get a figure of 900 billion tonnes of atmospheric CO2 for the present day, so one of is out by a factor of over 2.

    • Clive Best says:

      I am just using the mass of carbon. CO2 molecules have 2 extra oxygen atoms so the carbon component is roughly 30% of the total mass. Photosynthesis splits carbon from CO2.

      • Andrew Carey says:

        Any chance of re-doing the article so that point is clear in all cases where atmospheric quantities are mentioned. The reason for asking is that saying “billion tonnes of atmospheric CO2” when you don’t mean that and in fact mean C is confusing.
        I have the carbon component of CO2 as 12/44 or 27.3% roughly. 0.273 * 2147 gives 586, so still not getting close to your 900 figure I’m afraid.

        • Clive Best says:

          I changed the wording. Is that clearer now?

          • Andrew Carey says:

            It’s actually worse now Clive. The reason is that in the opening two sentences you say that there was 610 billion tonnes of C in the atmosphere in the immediate pre-industrial period. That gives a comparator to biomass-C (that’s just the C, not the carbohydrate, proteins and others, just the C within those molecules). Later you say that “Atmospheric CO2 has risen from 610 billion tonnes (280ppm) to 900 billion tonnes (417ppm)”. These are mutually incompatible claims. It’s either 610 billion tonnes of C, or 610 billion tonnes of CO2.
            As previously said I would also appreciate it if you could show your working for how you arrived at 900 billion tonnes of atmospheric CO2 for the present day because I can’t find it. TIA.

      • Andrew Carey says:

        I think I’ve worked it out now. Atmospheric CO2 is around 417ppm by moles or by molecules. However it is around 632 ppm by mass.
        Mass of atmosphere is around 5.1480×10 18 kg. Multiply and you arrive at approximately 3254 billion tonnes of atmospheric Carbon Dioxide. Multiply by 12/44 as C is 12/44ths of CO2 and atmospheric C is around 887 billion tonnes. (Close to the 900 number you incorrectly attributed to atmospheric CO2).
        Track back to pre-industrial, by multiplying by 280/417 and we have atmospheric C at around 596 billion tonnes (Close to the 610 number you incorrectly attributed to atmospheric CO2).
        However this *is* close to the pre-industrial Biomass-C number at the start of your piece.
        Mashing units of mass with moles, and C with CO2 isn’t good. Bit like mashing energy units with power units by many semi-literate politicians.

        • Clive Best says:

          We are now almost in agreement if you accept the following.

          1. I calculated 600 billion tonnes of carbon for a concentration of 280ppm of CO2 ! That is 900 for 417ppm of CO2. So we agree.

          2. The wording was confusing for CO2 level scaling. I only ever talk about the Carbon content of CO2 and never the mass of CO2 itself. Sorry for confusion. I have updated it.

          However you look at it the pre-industrial mass of carbon held in the atmosphere was basically the same as the living Biomass carbon.

          Furthermore this same relationship seems even to hold during the Carboniferous period. You are free to say this is a total coincidence but I doubt that it is. I think it is more likely that Photosynthesis maintains this balance.

    • Clive Best says:

      Yes you are right.

      Oceans are a sink that absorbs the excess anthropogenic CO2 in the atmosphere when the partial pressure increases above that at the ocean surface. CO2 then dissolves via carbonic acid (H2CO3).

      Yet despite covering 70% of the planet, oceans contain just 1% of carbon biomass !

      • piton says:

        however, in the report WG1AR5_all_final.pdf, chapter 6, page 487, we find in Figure 6.1 “Simplified schematic of the global carbon cycle. Numbers represent reservoir mass, also called ‘carbon stocks’ in PgC (1 PgC = 1015 gC) and annual carbon exchange fluxes (in PgC yr–1). »
        Current vegetation stock: 450 to 650 -30 i.e. 420 to 620
        Current stock atmosphere: 589 + 240 i.e. 829
        Current ocean surface stock: 900
        I don’t know how to send the schematic.

        • Clive Best says:

          This is all based on the BERN model which makes assumptions about rock weathering and deep ocean take up of CO2. Ice age cycles are currently every 80,000 years or so which implies a shorter CO2 cycle. Levels change from ~ 300ppm during an interglacial to 180 ppm in much less time.

          Here is the schematic

  6. Javier says:

    “These two are almost identical which in my opinion cannot be a coincidence.”

    You haven’t thought things over enough. C4 plants can photosynthesize efficiently at much lower CO2 concentrations therefore they will draw atmospheric CO2 lower than C3 plants. C4 plants are a relatively recent evolution. There is no reason why atmospheric CO2 amount should be similar to biosphere carbon amount.

    “Reforestation would probably be the quickest route to begin rebalancing carbon.”

    Unnecessary. The biosphere takes care of itself if we just leave her alone. The leaf surface expansion measured by satellites has been nothing short of spectacular. We couldn’t match it even if we tried.

    • Clive Best says:

      Trees are C3 and ~90% of living carbon is held in forests and temperate latitudes. I think C4 plants win out in dry arid areas because they rely less on H2O.

      If we could take humans out of the equation and leave nature to recover, then natural plant growth and geographic extent would bloom, fertilised by the excess CO2 and slightly warmer and wetter climate.

      The living biomass carbon atoms would then once again balance the carbon atoms bound within atmospheric CO2 molecules.

      The very slow geological carbon cycle would continue as always.

  7. Valterio says:

    Hello dr Best
    Hi I would like to know what you think of what your partner Madrigali writes on Facebook in his profile

    • Clive Best says:

      I once wrote a paper with him as coauthor on the impact of tidal forces on the Jet Stream but I have no idea what he writes on facebook !

      • He’s writing in Italian. The premise of tidal forcing is correct but missing how to do the fluid dynamics response correctly. Missing pieces are the annual impulse that syncs with tidal force at that time (related to monomictic or dimictic thermocline overturning), and the nonlinear transform that needs to be applied to fit the time series.

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