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I've got a friend who is a climate change sceptic.

He argues that because all the CO2 in fossil fuels originally came from the earth's atmosphere. Then there can't be a problem releasing the CO2 back into the same atmosphere.

Intuitively it seems obvious to me that the quantities CO2 was stored up over a long time and now is being released back into the atmosphere is just a few short decades which is causing problems but his counter is that the earth is a closed system and so the total amount of carbon CO2 is constant. This part I'm less sure on but I have a feeling he must be wrong on that too.

Can someone please explain where the flaw is his logic is? I want to debunk this in as scientifically accurate as way as possible.

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    $\begingroup$ It sounds to me like you've been lured into a debate about the details of the Earth science without agreeing what constitutes "a problem". No amount of evidence can counter-argue or convince someone from a position they haven't defined. Your friend probably hasn't even decided their position internally, and will just define and redefine it to remain not explained by your evidence. This is a rhetorical tactic rather than a logical flaw: the implicit straw man. $\endgroup$ – Deditos Apr 26 at 10:08
  • $\begingroup$ The answer below is detailed. However is not true that all the CO2 sequestered by fossil was once there all together, if we consider this world. Tell you friend that the world we are currently inhabiting was formed right by CO2 sequestration, which likely started by marine microorganisms and before plants. Putting the reasoning in the right mass and time scale should evidence that is argument is very poor, at least poorer than what the answer by @Erik suggests (answer that I up vote, by the way). At best your friend is right that the entire process might restart (but not given). $\endgroup$ – Alchimista Apr 26 at 10:59
  • $\begingroup$ The total amount of carbon is constant but obviously when you dig up coal and burn it you increase the CO2. $\endgroup$ – Keith McClary Apr 29 at 21:36
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First of all, earth doesn't have the same atmosphere it had, back when dinosaurs walked the earth, when most of current carbon-deposits formed. Some atmospheres earth had would even be toxic to humans. So, you're right, changing the atmosphere at the speed we're doing it is the problem, not the change in general.


Second, yes, earth is a rather closed system (with minor leaks, but anyway). Still, the timescale is important.

Let's go with a simple allegory:

Say, your friend had a pickup-truck (sorry, in my mind deniers all drive SUV or pickup^^). He uses it to transport a lot of material, e.g. paving stones. He knows, his truck is able to transport the total amount of stones (because he tried in the past, or because the specifications say so, or because someone told him, doesn't matter - like we know that earth's atmosphere held a lot more CO2 back in the day).

Is he going to just dump the whole load at once from 2 m height into the back of his truck? I doubt so, because that would at least put some dents in the truck, or might even break the springs or an axle.

He'd pack the stones there manually and use enough padding to make sure nothing gets damaged or slips during the transport.

Currently we're dumping the stones all at once - and we'll surely break the vehicle, if we really continue. Earth, like the truck, needs to adapt to changes. And, as we know, geological timescales are a lot longer than we can truly observe - thus the current changes, though stretching over several generations, are way too fast for earth to really adapt.


Third: While earth is a closed system, states within a closed system may change. Say, you have a terrarium with some mice and a lot of wood. Then you burn the wood. The mice might survive the fire, but in the end will suffocate, since there is a lot more CO2 in their atmosphere now.

So, yes, releasing trapped carbon from fossile fuels and whatnot to the atmosphere doesn't change the overall mass of system earth. But it changes the state of the system - and we are depending on the current state of the system.


Also - I know, this is not scientifically - say we are wrong when it comes to greenhouse gasses, and he is right. What if we undertook a lot of effort to not to produce them, to clean our environment, to create less waste? We'd wake up one morning and be "Dang, we made our planet worth living on again, how could we?!" - Or, as one of my professors put it: "Would you get on a plane when there is a 10 % chance, the plane is going to crash?"

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The total amount of carbon is constant, the total amount of CO2 rises, mainly due to the burning of fossil fuels.

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If you put a blanket around yourself, you warm up.

Sounds a bit silly, but this is the physics of GHG warming in a nutshell. The atmosphere is transparent to optical radiation which provides nearly all the energy to be trapped.
Therefore, when computing a GHG model, you can put the source of the heating actually onto the surface of Earth. The energy is then reprocessed into infrared radiation and tries to escape.

In this situation, both your body and the Earths atmosphere try to radiate in the infrared, but with a blanket that heat cannot escape anymore. No matter if the blanket was laying around somewhere else for thousands of years, in that moment it gets warm.

This is of course a flawed analogy, the better one is the one of the greenhouse: Visible light can enter, providing heat, but cannot escape in the infrared, because the glass is intransparent to infrared. The more $\rm CO_2$ there is in the atmosphere, the more 'glass'. No matter if this glass was buried underground for ages, at this very moment it causes temperatures to rise enormously.
Same story with why a car heats up into a death trap in summer, while the exterior of the car at the same moment doesn't.

Your friend (and probably other climate denialists) confuse the Earth's mass balance with its energy balance. One doesn't have much to do with the other.

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Something else to consider: the amount of energy we get from the sun is slowly increasing over the billions of years as the sun goes through its lifecycle, so when you go back to ancient atmospheres and find what we would consider very high concentrations of GHG like CO2, it was necessary at that time to keep the planet warm. You can't simply look at the atmosphere from half a billion years ago and compare it with the present without considering the solar output.

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