Given the fact that industries emit about 1.5 billion metric tons of carbon dioxide each year just in the US, why is it still such a small part of the atmosphere's composition (0.04%)?

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    $\begingroup$ It used to be 0.028% when I was young... $\endgroup$
    – fraxinus
    Nov 19, 2023 at 11:10
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    $\begingroup$ I parsed the title as low in altitude; that is relative CO2 concentration decreases as altitude increases; and got really curious. Was disappointed. $\endgroup$
    – Joshua
    Nov 19, 2023 at 15:24
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    $\begingroup$ I'd love an answer about why the CO2 levels are such a small percentage independent of human-made emissions. I suppose it is related to biological or geologic processes over the past few billion years. $\endgroup$
    – bigchief
    Nov 19, 2023 at 19:59
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    $\begingroup$ @bigchief feel free to post a question $\endgroup$
    – fraxinus
    Nov 20, 2023 at 8:05
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    $\begingroup$ if you want global industrial production that's about 3 billion tons, ourworldindata.org/emissions-by-sector and of course that is ignoring manufacturing and electricity production. $\endgroup$
    – John
    Nov 20, 2023 at 23:59

3 Answers 3


The mass of the atmosphere is 5.1 × 1018 kg, which is 5.1 × 1015 t.

As stated in the edited question,

industries emits 1.5 billion metric tons of carbon dioxide each year,

That's 1.5 × 109 t.

The mass of Earth's atmosphere is 3,400,000 times the mass of CO2 that industries produces each year in the US.

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    $\begingroup$ @MarkRansom the original article is in metric tons $\endgroup$ Nov 19, 2023 at 14:39
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    $\begingroup$ @AlanBirtles I was unaware that the abbreviation of metric ton was also t. Thanks for straightening me out. $\endgroup$ Nov 19, 2023 at 14:56
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    $\begingroup$ Hmmm using worldwide CO2 concentration and US CO2 emissions. That's weird. $\endgroup$
    – Joshua
    Nov 19, 2023 at 15:25
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    $\begingroup$ @SolomonSlow: Neither do I. I think it should be worldwide CO2 concentration and worldwide CO2 emissions. $\endgroup$
    – Joshua
    Nov 19, 2023 at 19:33
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    $\begingroup$ @Joshua : the question specifically asked why it is low despite those 1.5 billion tons. This answer shows exactly those 1.5 billion tons in perspective, therefore it answers the question better than if it used global emissions. Even if the answer was expanded to include global emissions, it needs those 1.5 billion tons, so that the OP can see how it relates. $\endgroup$
    – vsz
    Nov 20, 2023 at 9:10

As well as the atmosphere having a lot of mass, there are many processes which remove CO2 from the atmosphere, see the wikipedia article for the carbon cycle. Plants sequester it as biomass, some of which ultimately ends up in the soil long-term (the rest is either released again by organic decay or fires). The ocean also absorbs a lot, which is related to the problem of ocean acidification you may have heard of.

It's a delicately balanced dynamic equilibrium that we are disrupting, not a static situation. Think of it like a sink with a half blocked drain that's slowly filling up as you run the water, rather than an empty bowl you're filling up.


"Small" is a vague and slippery term. There is now a lot more CO2 in the atmosphere than there was a century ago and that change has consequences, especially to climate stability. There is a lot more human emissions - around 40 billion metric tons per year globally now - and that is causing atmospheric concentrations to rise. Those emissions are in addition to natural sources and are moderated by natural processes that absorb and recycle Carbon and overall, so far, natural processes have been taking CO2 back out of the atmosphere at rates greater all the natural CO2 flow into the atmosphere, or the human addition would be making concentrations rise faster than they are.

This diagram shows The Carbon Cycle. It is a few years out of date - the amounts of fossil fuel burning and other numbers will have changed a bit but it gives a good overview of where the carbon is coming from and going to.

Global Carbon Cycle


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