2010-09-20 06:31:30INTERMEDIATE Rebuttal 129: Breathing contributes to CO2 buildup.
Notes: Intermediate or basic - what do you think?

What the science says...

By breathing out, we are simply returning to the air the same CO2 that was there to begin with.

The very first time you learned about carbon dioxide was probably in grade school: We breathe in oxygen and breathe out carbon dioxide. Any eight-year-old can rattle off this fact.

More specifically, the mitochondria within our cells perform cellular respiration: they burn carbohydrates (in the example shown below, glucose) in the oxygen that we breathe in to yield carbon dioxide and water, which we exhale as waste products, as well as energy, which is required to maintain our bodily processes and keep us alive.

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

carbohydrates + oxygen → carbon dixoide + water + energy

It should come as no surprise that, when confronted with the challenge of reducing our carbon emissions from the burning of fossil fuels, some people angrily proclaim, "Why should we bother? Even breathing out creates carbon emissions!"

This statement fails to take into account the other half of the carbon cycle. As you also learned in grade school, plants are the opposite to animals in this respect: Through photosynthesis, they take in carbon dioxide and release oxygen, in a chemical equation opposite to the one above. (They also perform some respiration, because they need to eat as well, but it is outweighed by the photosynthesis.) The carbon they collect from the CO2 in the air forms their tissues - roots, stems, leaves, and fruit.

These tissues form the base of the food chain, as they are eaten by animals, which are eaten by other animals, and so on. As humans, we are part of this food chain. All the carbon in our body comes either directly or indirectly from plants, which took it out of the air only recently. 

Therefore, when we breathe out, all the carbon dioxide we exhale has already been accounted for. By performing cellular respiration, we are simply returning to the air the same carbon that was there to begin with. Remember, it's a carbon cycle, not a straight line - and a good thing, too!

2010-09-20 06:39:05Great post
John Cook


For some reason, I found myself humming the Lion King's "Circle of Life" while reading this :-)

I would suggest intermediate because of the chemical equation although the basic version would be pretty much the same thing without the equation. 

Maybe the basic version could feature a simple graphic. I can whip one up for you if you like, similar to the carbon cycle graphic.

2010-09-20 06:45:43
Rob Painting
"Any eight-year-old can rattle off this fact." - made me laugh, that did.
2010-09-20 06:52:19BTW, this is a good rebuttal to Ian Plimer
John Cook

One of Plimer's favourite jokes when public speaking is how we exhale CO2 so AGWers should stop breathing. When he used that joke at the Monckton/Plimer debate, Monckton nearly wet himself with laughter. A real crowd pleaser (considering the crowd was mostly skeptic).
2010-09-20 07:58:008-year-olds
Dana Nuccitelli

I find it hard to believe that anyone above the aforementioned age of 8 finds that joke funny.

Nice job, Kate.  This could work as either basic or intermediate level.  I agree with John, perhaps the chemical formula makes it intermediate, and a carbon cycle graphic would help.  This is a good one:


2010-09-20 17:43:19

Leave out mitochondria and carbohydrates and it's a great grade school level rebuttal :)
2010-09-20 20:29:06
Ari Jokimäki


"All the carbon in our body comes either directly or indirectly from plants, which took it out of the air only recently."

However, if the world population increases and the amount of vegetation decreases, then there might not be a plant anymore to take out the carbon dioxide of the air I exhaled. In that situation there should be a net carbon dioxide emission from human breathing, I think.

2010-09-21 02:32:20but in that case

you won't have anything to eat, so you're output will soon cease, I'm afraid.
2010-09-21 03:06:39
Ari Jokimäki


Yes, but isn't that exactly what we are doing right now, each year we use that year's world resources earlier and earlier.

2010-09-21 04:54:18

Actually, I find that graphic more difficult to understand than the chemical equation...

I think the first time I encountered the equation was in grade 8 with words, and grade 9 with element symbols.

So should we make 2 very similar ones, or make this one basic (maybe change a few words as suggested) and then see what we can expand on for the intermediate? I'm not sure, as this rebuttal isn't very complicated and I'm not sure how much more detail we could go into...

Thanks for the feedback


2010-09-21 07:09:22Simpler graphic
John Cook


For a carbon cycle, I was thinking something much more simpler, giving just the bare basics to explain the principles in your post. Eg, here's a rough (very rough, emphasis on rough) sketch of what it might include:

So if this is on the right track, Kate, let me know what changes you'd like made to it and I'll do up a more professional version.

2010-09-21 10:33:19
Chris Colose

Except the human above is a vegetarian...just unacceptable :-)
2010-09-21 13:39:34Vegetarian
John Cook


I'll draw a bite mark out of the animal :-)

Actually add an arrow from animal to human. Figure needs a heading too - what would you call this? Respiration Carbon Cycle?

2010-09-22 00:32:41Rebuttal 129: Breathing CO2Thumbs up


Good rebuttal. I think colored carbon cycle diagram is too complex for basic, but fine for intermediate version. I think John's diagram is perfect for basic, with arrow from dog to man. By the way, why are we eating a dog?



2010-09-22 02:05:21Good rebuttal
James Wight

Welcome aboard, Kate.

I agree with the others that a basic rebuttal would exclude the chemical formula.

Regarding John’s diagram, I think it should also include arrows labeled “O2” for plants breathing it out and humans breathing it in, and the arrows from plants to animals should be labeled “C”.

Ari Jokimäki, the decrease in the amount of vegetation would come under deforestation, which is included in the carbon budget. As for the increase in human population I’m not sure it makes that much difference considering all the other animals breathing out carbon dioxide.
2010-09-22 09:28:50

John, I agree with the other suggestions as to the diagram, but I think it's on the right track. Perhaps a cow instead of a dog, and grass instead of a tree (as dogs don't really eat trees)? I think a heading of "Carbon Cycle" would be fine.

So it sounds like we are going to make two very similar versions for basic and intermediate - am I right on that? Would you like me to make the quick changes for the basic version and/or post it separately?



2010-09-22 10:23:02Cow instead of a dog
John Cook


Umm that was meant to be a cow. Hey, it's not easy drawing with a mouse! :-)

If you could do two similar versions, that would be great - with the intermediate just a little more detailed than the basic version. Will post up a pic for you shortly.

2010-09-22 12:47:26How's this graphic? (apart from it looks like the cow is farting on the human)
John Cook


I went real simple, opted not to include James' suggestions of including O2 exhalations and labelling the plant to animal as C. If this is too simple and people feel it should have the other details, let me know. Or perhaps have the more complex version for the intermediate version?


2010-09-23 08:54:02

I agree, it is the carbon cycle, not the carbon and oxygen cycle, that we are focusing on.

I will write the basic version tomorrow evening.


2010-09-23 18:52:57
Otto Lehikoinen
lol, I like John Cook's first graphic best, but agree there should be an arrow from the cow, too. Also, one could say "fossil fuels can't be eaten". That should go well with those who have for whatever reason had to empty their gas tanks.
2010-09-26 14:00:33Published
John Cook

Have used the intermediate version as the blog post, also included a link to the basic version. Thanks for this Kate!
2010-09-26 16:54:00

ready to go
2011-01-22 11:37:17
Shirley Pulawski

It's funny - this topic just came up in discussion in one of my classes - whether or not exhalation contributes to increases in CO2. I had to also wonder to what degree our bodies also sequester carbon since we are carbon based life forms and most of what we consume (carbs, proteins, etc) are carbon based. 

Also, I've never researched anything like this, but are there data out there which would compare the amount of CO2 typically exhaled by an adult to the carbon release of other activities, like running a small electric fan, air conditioner, hair dryer, etc. If you could find something like that, the scale of contributions might be easier to understand.  

I think this makes for a very good intermediate rebuttal, but I'm not comfortable with the opening statement, "By breathing out, we are simply returning to the air the same CO2 that was there to begin with." To me, that isn't quite true and not really what the rest of the answer supports. I think it's a line that could be manipulated to argue that burning coal is just returning the CO2 that was already out there. I think something that explains that the net budget of carbon intake and released is somewhat balanced, and that our other activities (driving, heavy agriculture, electrical consumption, etc.) contribute much more to increasing atmospheric CO2 levels. 

2011-01-22 19:43:58Timescale?


Hi Shirley,

while translating the argument/soundbite into German I also briefly thought about the opening sentence and that it was a bit vague. Perhaps simply adding something: "By breathing out, we are simply returning to the air the same CO2 that was there to begin with a short time ago." From my understanding, this is the big difference: the CO2 emitted by burning fossil fuels had been safely sequestered for a very long time (hundred-millions of years) and we now dump a lot of it back into the atmosphere in a very short time.