If carbon dioxide increases its percentage in the atmosphere (eg from 0.03 % to 0.045%) does this mean that the total mass of the atmosphere increases? If not, then does the extra percentage of carbon dioxide occur with a corresponding decrease in some other gas in the atmosphere? Simple question but one that requires an answer.
Since we are converting solids and liquids into gas, the CO2 and methane are increasing the total mass of the atmosphere, because the loss to space is only 90 tons a day, which means it is a tight envelope around the planet.
Interesting question. I don’t have a definitive answer, but I think that Craig Carlton Dremann response is missing an important piece of the answer; it’s not as simple as “fossil fuels are removed from the ground and end up as CO2 in the atmosphere.”
In the process of burning fossil fuels, CO2 is produced (making the atmosphere heavier) while atmospheric O2 is consumed (making the atmosphere lighter). Indeed, the concentration of atmospheric O2 has been declining … and at a faster rate than CO2 has been rising (I estimate a ~4 ppm/yr decline in O2 vs. a ~2 ppm/yr rise in CO2 from 1992-2012; attached figure is from Chapter 6 of the IPCC Working Group 1 report from 2013). So, if this is all that was happening in the atmosphere, I’d say that the atmosphere was getting lighter.
However, the concentrations of other gases are also changing. Methane and N2O are increasing due to human activities (although this is trivial with respect to the mass of the atmosphere due to their low concentrations). More importantly, the amount of water vapor in the atmosphere is rising because the atmosphere is warming. If Wikipedia’s article on water vapor is correct and the global average water vapor concentration is ~0.25% by mass (or ~4000 ppm on a molar basis) and is increasing at 1-2% per decade (or 4-8 ppm/yr), then the net result is that the atmosphere is getting very slightly heavier...which turns out to be the same answer Craig provided earlier.
My math follows:
Annual change in CO2:
+2 umol CO2 / mol air * 44 ug CO2/umol CO2 = +88 ug CO2/mol air
Annual change in O2:
-4 umol O2 / mol air * 32 ug O2/umol O2 = -128 ug O2/mol air
Annual change in H2O vapor:
+4–8 umol H2O / mol air * 18 ug H2O/umol H2O = +72 to 144 ug H2O/mol air
Overall annual change per mol air = +88 ug CO2 – 128 ug O2 + (72 to 144) ug H2O = +32 to 104 ug gas
Very elaborate analysis. Thank you Scott. I wonder if the increase of O2 emission due to higher photosynthesis should participate in calculations. Finally someone should give a recent percentage allocation of gases in the present atmosphere.
You're welcome.
No, you don't need to include O2 from photosynthesis in the kind of calculations I did because it is already in there. The measured change in atmospheric O2 is the net result of every process that could affect O2 (removal via fossil fuel combustion and respiration, addition via photosynthesis, exchange with ocean and freshwater, etc.).
NASA has an "Earth Fact Sheet" webpage, which includes the composition of the atmosphere. It was last updated in Dec 2021 so its numbers might be recent-enough for your purposes.
Scott C. Neubauer -- Excellent answer, I just did not sit down and do the math, but of course when you burn carbon to produce CO2 you grab the O2 to make CO2 you are adding mass. The wild card is the methane from domesticated animals and from fossil fuel production and transportation--we have an equal amount of cattle biomass on the planet as we do humans, and those cows burp a lot of methane plus their poop is adding to the mass of the atmosphere too. And wherever we are drilling for oil, we release a lot of trapped underground methane that is also adding to the mass of the atmosphere. And burning any fossil fuel or organic materials like wood, peat, etc., also adds mass.
According to Trenberth & Smith (2005), The Mass of the Atmosphere: A Constraint on Global Analyses
DOI: https://doi.org/10.1175/JCLI-3299.1
the total mass of the atmosphere varies predominantly in response to the water vapour loading.
Concerning the influence of CO2 on the mass of the atmosphere I think that the effect is almost negligible although the calculation involved in the proof are rather complicated. Please consult the discussion on the physics stack exchange posted at:
https://physics.stackexchange.com/questions/65923/is-the-total-mass-of-earths-atmosphere-essentially-constant-in-time
Does movement of extra mass to the atmosphere via water and fossil gas have a significant effect on the speed of rotation?
https://www.sciencedaily.com/releases/2010/03/100308203308.htm
Geoff Pain
According to the discussion in the physics stack exchange mentioned above the change due to the trace gases is less than a fraction of a nanosecond per year.
Much larger changes of the length of day are associated with melting of glaciers
"As glaciers melt and ocean levels rise, Earth rotates slighter faster every day, making this an unexpected challenge in the era of climate change".
Source:
https://inkspire.org/post/climate-change-is-making-the-earth-spin-faster-what-does-this-mean-for-us/
Thanks Janusz Pudykiewicz
Have you come across data on Carbonic Acid H2CO3 content of the atmosphere?
Dear Geoff Pain
I will try to check the most recent data but please read the following discussion
https://chemistry.stackexchange.com/questions/121525/does-co2-form-carbonic-acid-in-the-atmosphere
I am happy that my initial question triggered such a fruitful scientific dialogue among eminent coleagues.
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