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I'm not talking about other artificial human activities like fossil fuels or cars or cattle farming. I meant just in terms of breathing, how much did the CO2 level of the earth increase because of the recent overpopulation, and is it significant?

Like let's just say hypothetically that I stopped existing, how much global warming would I be saving?

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Human and animal respiration has no global warming impacts. The CO2 released by respiration is in balance with the CO2 absorbed by the plants that became the foods that were the source of the CO2 released by breathing.

With the production, storage, transport and processing of foods for humans and domesticated animals there are emissions that are derived from fossil fuel burning, that are in addition, and are not balanced by food plants absorbing CO2.

Food and respiration

(image from Veritas Press)

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    $\begingroup$ This work as long as there is no overshooting of the resources... $\endgroup$
    – EarlGrey
    Commented May 1, 2023 at 11:59
  • $\begingroup$ > "The CO2 released by respiration is in balance with the CO2 absorbed by the plants" Is that still relevant due to mass logging and cutting down of rainforests? $\endgroup$ Commented May 5, 2023 at 9:14
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    $\begingroup$ @DavidNyan10 - the question was specifically about the climate impacts of human respiration. I made mention of the emissions in addition (that are not derived from CO2 drawn out of the atmosphere by plants) from FF's use in modern agriculture and food supply chains but yes, there are non-FF emissions including the impacts of deforestation. AGW isn't directly a pop. problem, it is a per capita emissions problem; without zero per capita it would take zero population to reach zero, ie not an acceptable solution. $\endgroup$
    – Ken Fabian
    Commented May 5, 2023 at 22:19
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The average adult person emits 0.66kg per day (0.3 Tons per year).

Given the current population, 8 billions people, this translates into 2 GTon of CO2 per year.

Rough estimates of our impact on the atmoshpere gives our CO2eq emissions at aronud 40 Gton of CO2 per year. 10% of it is therefore directly related to our breathing.

Sources: here and reference therein: https://www.newscientist.com/lastword/mg25534022-700-what-percentage-of-carbon-dioxide-emissions-is-from-us-breathing-out/#:~:text=If%20we%20roughly%20estimate%20that,into%20the%20atmosphere%20each%20year.

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    $\begingroup$ Sorry, incorrect. Any change to global CO2 concentrations and therefore climate impacts comes from the difference between the Carbon as CO2 that food plants absorb and the CO2 human respiration makes from that food. Effectively zero. The link requires registration to read - so didn't - but I would be surprised if the article failed to make that distinction clear. If not, the article is misleading. $\endgroup$
    – Ken Fabian
    Commented May 1, 2023 at 22:00
  • $\begingroup$ @KenFabian Google's cached version indeed does show that... seems more of a Q and collected answers site than an article. Response one doesn't mention the cycle (but also calculates the 40GT as only 4%). Response two says "The carbon dioxide we breathe out is used by plants to grow through photosynthesis, as part of the carbon cycle." Response three says "Human exhalation is part of the natural cycle of gases entering and leaving the atmosphere, so it doesn’t produce any overload per se. But we do contribute via our diets, as food production causes about a third of carbon emissions." $\endgroup$ Commented May 2, 2023 at 20:15
  • $\begingroup$ @KenFabian your description it's a bit of zero-order asymptote ... we cannot have enough plants for every living human, if we do not have industrial agriculture. Without industrial agriculture, not all of the exhaled CO2 would be adsorbed by plants ... because there would not be enough plants $\endgroup$
    – EarlGrey
    Commented May 2, 2023 at 21:01
  • $\begingroup$ Around here plants grow by themselves, pretty much everywhere, whether we want them or not; a lot of agricultural land has less vegetation, including periods of ploughed back to zero, than if left uncultivated. We won't have enough food without industrial agriculture but plants are enough to deal with all the CO2 made by humans from ingested food - and what plants take in and what respiration produces are effectively in balance. $\endgroup$
    – Ken Fabian
    Commented May 3, 2023 at 1:52
  • $\begingroup$ @KenFabian yes, eating the plants that grows around you, you can live with a diet of about 500 kcal per day. Enjoy! $\endgroup$
    – EarlGrey
    Commented May 3, 2023 at 6:23

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