What effect would having CO2 in your atmosphere in place of, on earth, Nitrogen have on the carbon cycle? would the carbon cycle even work? I'm engineering A theoretical tidally locked planet with an atmosphere of 0.9atm, and 49% CO2, 40% O2, 10% N2, and 1% SO2.

  • $\begingroup$ What sort of effects are you looking for? Effects on Life? plants? geology? $\endgroup$
    – Shadowzee
    Commented Feb 27, 2019 at 1:29
  • $\begingroup$ Earth had a high CO2 content over the course of its lifetime, and there has been no ceasing of the carbon cycle, just as the nitrogen cycle hasn't stopped even though our atmosphere is about 70% nitrogen. $\endgroup$
    – Bewilderer
    Commented Feb 27, 2019 at 1:31
  • 1
    $\begingroup$ effects on weather cycle, mostly. $\endgroup$
    – Leo Fisher
    Commented Feb 27, 2019 at 1:49
  • 3
    $\begingroup$ You of course know humans can't live on this planet unprotected, right? At those partial pressures, your humans will die of oxygen toxicity and CO2 poisoning simultaneously and almost instantly. This is not a nice place to live. $\endgroup$
    – Tim B II
    Commented Feb 27, 2019 at 2:03
  • $\begingroup$ A major factor in Earth's carbon cycle is temperature at sea level. Without knowing that, it is impossible to say what your planet's carbon cycle will be like. $\endgroup$ Commented Feb 27, 2019 at 2:14

2 Answers 2


You might be interested in something like gas exchange in the lungs

The partial pressure of carbon dioxide is also different between the alveolar air and the blood of the capillary. However, the partial pressure difference is less than that of oxygen, about 5 mm Hg. The partial pressure of carbon dioxide in the blood of the capillary is about 45 mm Hg, whereas its partial pressure in the alveoli is about 40 mm Hg. However, the solubility of carbon dioxide is much greater than that of oxygen—by a factor of about 20—in both blood and alveolar fluids. As a result, the relative concentrations of oxygen and carbon dioxide that diffuse across the respiratory membrane are similar.

The reason we are able to exhale carbon dioxide is that there is a greater gas pressure difference in CO2 in our body than in the atmosphere. WIth a higher concentration of CO2 in the atmosphere, our gas exchange system does not work. The body can not get rid of CO2.

So if you are talking about plant and animal life as we know it on earth, it would not survive such an atmosphere. However, that is not to say that if this atmosphere DID exist on earth, life could not have evolved under such conditions. At the least, blood chemistry would be very different. Our lungs are designed so that, under our atmosphere and atmospheric composition, our system is balanced between oxygen intake and CO2 expulsion. I would posit that, under such an atmosphere, and under these gas pressure differentials, a higher functioning organism might perhaps have TWO gas exchange 'lungs' - one for the absorption of oxygen, and the other for expulsion of CO2, and the respiration rate of these two lung systems would not necessarily be the same. One might be breathing faster than the other, or one might be significantly larger than the other.

But once a mechanism is developed for maintaining the correct balance of CO2 and oxygen in the body, I am not sure much else would be different.

The same would go for photosynthesis and nitrogen uptake by plants. The mechanisms would certainly be much different than that for earth-based systems, and there might be a need for greater differentiation, a radically different comparative size of the systems, and such. For instance, plants breathe on the under surface of leaves, photosynthesis occurs on the top surface, so leaf geometry would certainly be different at the least. But once the correct balance of gasses was established internally, the chemistry could proceed as in a normal carbon cycle.


Because of Henry's law the $C$ concentration on oceans would be bigger than at Earth. At oceans $\small\sf{CO_2}$ is chemicaly in the forms $\small\sf{HCO_3}^{2-}$ and $\small\sf{CO_3}^{2-}$ with the concentrations you can show in this link. At your planet, they would be bigger because of the quoted chemical law that says there is a temperature-dependent equilibrium between dissolved gas on the interface water/atmosphere.

The other main part of Carbon Cycle at Earth is biochemical:

So in your planet this part of the cycle could be developed resulting a bigger chemical flux. Also if organisms form skeletons, there would be calcite/aragonite (and maybe dolomite) on sedimentary cover.

A different question is what kind of life would be at a non-atmospheric $N$. Proteins and DNA have it on their structures. $N$ enters on the flux thanks to denitrifying bacteria that fix it for other organisms, so there migth be a different kind of life. If so, and it were $C$ based life, there would be more biomass in general.


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