At what concentration does CO2 become toxic to humans?

Written by Dr. Darko Butina


Or, What is the difference between the engine that runs the human body and the combustion engine? None!

The molecule carbon dioxide (CO2), a trace gas in our atmosphere is just about reaching concentration of 400 parts per million or 0.04%, as measured at the Mauna Loa Observatory, better known as MLO. The current public view of CO2 is that of a villain causing practically everything that is wrong on our planet, from prostitution to tsunamis, from schizophrenia to earthquakes, from overheating to overcooling, from floods to droughts and so on.

Since well over one thousand peer reviewed papers say so, since all of the major television and newspapers outlets say so, since lot of national academies say so, surely it must be so? Surely, to accuse someone of mass murder and even genocide one would expect overwhelming evidence against the CO2 molecule; not by thousands of unreliable witnesses that never met or saw the murderer, but by the hard forensic data, in this case experimental data.

Since the standard definition of excellence in the climate sciences is ‘the less you know about CO2 and the calibrated thermometer, the more eminent scientist you are’, I will humbly present to you some basic facts about CO2 that all those “ignorant specialist” in respiratory mechanisms and carbon chemistry are using in their daily jobs of pushing the frontiers of science forward, not backwards.

This report is about toxicity of CO2 and I will answer that infamous $64,000 question, or the way that the things are going at the moment, $64 trillion question: At what concentration does CO2 become toxic to humans?

So let me start with the first question raised in the title of this report. You see, there is no difference between the engine that runs the human body and the combustion engine – they both run on the molecules that are based on the element called carbon with the symbol C, they both need the O2 molecules to break the fuel down to smaller chunks, or rather oxidise the fuel/food that is needed for the engine to run, and they both produce CO2 as a product of that oxidation process. For every single carbon that enters that engine (human body or combustion engine) one molecule of CO2 comes out.

Let us now turn to the medical sciences and our knowledge of the respiratory mechanism that is the key to our survival. For a long time scientists working in the field of human physiology have wandered why evolutionary forces made humans breathe out and assign the function of breathing in and out to the brain?Whether you are awake or asleep, every breath in is followed by the breath out – why is that?

We could easily understand breathing in – the human body cannot function without oxygen and therefore we should be OK by just breathing in. The answer became obvious once we realised that all life is based on the carbon atom with the molecules of DNA and proteins being the two main engines of that life. Since everything that supports life is based on carbon, it follows that the major fuel which runs the human engine needs to be based on carbon. For clarity, whether you eat meat or are vegetarian, you are consuming carbon! And then the knowledge of chemistry comes in – oxygen function is to ‘oxidise’ and since all the food is based on carbon, the result is CO2: C + O2 = CO2. It therefore follows that inside your body lots of CO2 has been produced as a by-product which needs to be taken out of the body – hence breathing out. As any textbook on respiration will tell you:

“The primary function of the lungs is to obtain oxygen for use by the body’s cells and eliminate the carbon dioxide that cells produce”.

The figure at the top of the page below shows the general principle of the exchanges of different gases that occur between the lungs and the blood stream:

Let me now bring in Dalton and the gas law named after him which is formulated in the following way:

p = p1 + p2 + p3 + …

where p is the total or measured pressure and p1, p2, … are the partial pressures of the individual gases.

For air, an appropriate form of Dalton’s law would be:

p(air) = p(N2) + p(O2) + p(CO2) + …

Let me slightly digress here and explain to non-scientists what the scientific laws are about. Unlike any law in everyday life which is formulated and defined by the committee of experts and politicians ( i.e. criminal law, and varies from one country to another country), the scientific laws are ‘extracted’ from the experimental data and the observations and then formulated by scientists. In case of Dalton, he made those observations back in 1800 but he had nothing to do with them being called after him, since it took another hundred years of observations by hundreds of other scientists – all observing the same thing for those observations to become scientific law. All the scientific laws have one thing in common – there is NOT a single observation in the published literature that fails the scientific law, because if there is one that fails it and it can be reproduced then the law is no longer a law and it is withdrawn from our knowledge database.

In the last 3 years, since I began trying to understand the mystic ways that the climate community is conducting their science, I came up with a very simple way to compare their climate science with real science – real science works on the principle that the science laws are absolute, that the physico-chemical properties of molecules are absolute and that the only way to measure the temperature of molecules is by using a calibrated thermometer. Meanwhile, it appears, the climate sciences stay away from all approved instruments as if they are infected by plague. They ignore scientific laws and use bits of (or none at all) of the physico-chemical properties of molecules, depending what the outcome of a particular computational simulation is needed. And they definitely do NOT measure things since the instrumental data has this habit of falsifying everything that their computers are producing.

But, back to the real science. In medical sciences 1 atmosphere, i.e. the pressure of the air at the sea level is expressed as 760 millimetres of mercury, 760 mm Hg. So, if we assume that the air consist of 78% N2, 21% of O2 and 0.04% of CO2 then each of the three molecules exerts the following pressure:

N2: (78/100)*760 = 593 mm Hg

O2: (21/100)*760 = 160 mm Hg

CO2: (0.04/100)*760 = 0.3 mm Hg

Now we need to make connection between the partial pressure of CO2 in the air and in the blood, before breathing in and after breathing out. For the gas molecule to cross from the lungs to the blood it needs to have the higher partial pressure in the lungs than in the blood, and obviously, the opposite is true – if the partial pressure of the gas molecule is higher in the blood than in the lungs, it will cross from the blood to the lungs. When it comes to CO2, its concentration in the blood, after the blood has collected all the CO2 generated by the bio-chemical process keeping the cells alive reaches the pressure of 45 mm Hg, while the pressure inside the lungs after we breathe in the air is 0.3 mm Hg.

Therefore, as long as the partial pressure of CO2 in the air that we breathe in is less than 45 mmHg, the human body will be able to clear out the cell-produced CO2. By the way, when people suffer serious brain damage which affects breathing, the function of those machines that maintain the life is to bring in the oxygen and make sure that all the CO2 is cleared from the blood stream.

The number to watch for is 45 mm Hg of CO2 in the air, or 6% or 60,000 PPM – that is the concentration of CO2 that needs to be reached for the humankind to become extinct. If my math is serving me right, if we divide 60,000 PPM with 400 PPM we get the ‘kill factor’ for CO2: 150.

In other words, the concentration of CO2 needs to increase 150-fold for the CO2 to become toxic.

Bearing in mind that all those mathematicians and paleo-something scientists do not have a clue about the real capacity of the CO2 sinks, like the water and the biomass (more about it in the next report) I reckon that we are perfectly safe for a long, long time and should celebrate CO2 as a gas of life. If it was not for CO2, we would not be discussing it today.

The reports to come:

How does the CO2 molecule travel from LA to MLO which is over 4000 km away and at altitude of 4km?

How can we survive the Christmas meal in a deadly atmosphere of the CO2 concentrations reaching massive 3000 PPM?

Did you know that every time you cut the grass in your garden you generate over 10,000 PPM of CO2!!!

Stay tuned. More from Dr. Butina at his blog

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Comments (16)

  • Avatar



    Also it is the concentration of CO2 in our blood that controls the breathing reflex and surprisingly not a lack of oxygen.

    A basic Physiology 1 experiment to demonstrate this consisted of a student breathing recycled air filtered through lime water to remove the CO2.

    As the concentration of O2 diminished in the recycled air the student calmly started to lose consciousness from diminishing oxygen – no panic reaction provided the body was able to rid itself of CO2.

    That experiment I witnessed in the late 70s would probably fail Workplace Health and Safety guidelines today.

    Illustrative though.

    The final comment in the article is illustrative as well.

    Just how do climate scientists calculate the amount of energy used in converting simple gases into complex hydrocarbons, proteins and cellulose in their simplistic energy balances ?

    Einstein showed that even small amounts of mass contain enormous quantities of energy all built through photosynthesis.

    You can confirm the energy available by burning a piece of wood.

    Every week in summer my few hundred square metres of lawn produces several kilos of lawn clippings – there is an enormous amount of energy bound in this.

    Do they account for this ? How ????

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    That energy can be “captured” without any thermal effect proves another climate “science” claim wrong.

    “Trapping” energy does [b]not[/b] necessarily mean increased temperatures

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    I hear the accusation “That is a straw-man argument” about this argument or that argument all the time; it gets thrown around all the time, it is misused. THIS article is the best example of a bona fide quintessential straw man that I have seen in SUCH a long time.
    The problem with CO2 is not that it is toxic, that it is a poison gas that will asphyxiate or otherwise kill us all if we breathe too much of it. No one, NO ONE is arguing that the nature of the problem of CO2 emissions is that it will poison us. The problem is climate change, or global warming, is what they say. I tend to agree with them but I reserve judgement.
    Also if you could clarify the significance of the point that we release 10,000 ppm of CO2 every time we mow our lawn. I detect a hint of sleight of hand there, but I will give you the benefit of the doubt.

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    Climate scientists are NOT saying that CO2 is toxic. If you think that, then you do not understand climate science or the history of climate science.

    Climate science is concerned with the physical properties of CO2 which will affect everything on the planet, oxygen breathing or not. CO2 acts as a greenhouse gas – i.e. it traps HEAT in the atmosphere. If there were no CO2 in the atmosphere, the planet would be cold and dead.

    This article does not get it. It has no idea what it is trying to prove or what climate science is all about.

    • Avatar

      Ed Evans


      Hello Chemist having read your response that without co2 in the atmosphere the planet would be cold and dead? You could be right on one aspect , the dead bit. But cold? You clearly have no understanding of thermodynamics? The planet would still warm and cool during its daily cycle. The sun radiates heat. Please try again with more sound science.

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    Greg House


    [quote name=”chemist”]CO2 acts as a greenhouse gas – i.e. it traps HEAT in the atmosphere. If there were no CO2 in the atmosphere, the planet would be cold and dead.[/quote]

    In fact, the IPCC’s concept is that the Earth surface warms itself with twice as much power as the Sun does, “greenhouse gases” serving as passive reflectors. The relevant links to the IPCC’s “greenhouse effect”:, (2nd report) and An absolutely crazy idea.

    • Avatar

      Ed Evans


      Very strange how I always feel colder at night than during the day? Can anyone explain this phenomenon to me?

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    Oh my goodness! Impressive article dude! Many thanks, However I am going through issues
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  • Avatar

    eddie too


    this is probably obvious from my question, I am not a scientist.

    if the climate alarmists are correct about CO2 trapping heat on earth, why does it not also shield the earth from heat from outer space in the same manner?

  • Avatar



    Hmm… You might want to think a little more about this statement, since it’s not true:

    All the scientific laws have one thing in common – there is NOT a single observation in the published literature that fails the scientific law, because if there is one that fails it and it can be reproduced then the law is no longer a law and it is withdrawn from our knowledge database.

    There are many cases where scientific “laws” are just approximations and have exceptions in the literature. For example, Newton’s laws of motion break down and fail at relativistic speeds, but they are still considered “laws”, as they are a good enough approximation for many useful situations.

    Dalton’s law, which you reference applies to ideal gases, but not to reactive or condensing gases (most real gases that we deal with in the real world). It is still useful, and thus considered a “law”, but it has plenty of exceptions.

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    Dr. Darko Butina, thanks for the article, if I have a criticism it is imprecise terminology, (apologies if I do the the same!).
    There is a slight-of-hand going on-
    it is correct to say that carbon dioxide is ’emitted’ by certain industrial and natural processes. Then the word develops into ‘pollution’. Despite what ‘chemist’ says, words such a ‘toxic’ and ‘poison’ are used by climate alarmists. Further, neither the atmosphere nor its constituents trap heat, molecules radiate energy in all directions not just in the direction from which there is incoming radiation.

    Now, to my knowledge, carbon dioxide is not poisonous to animal life, at very high concentrations it does interfere with respiration and consciousness however. That is why it is used as part of so-called painless slaughter in abattoirs.

    Another point of interest as ‘Rossco’ observes, lawns (typical of vegetation) receive and store energy. The amount of energy stored is not indicated by the temperature of the lawn.

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    King Darius


    Forgive my lack of vocabulary and writing skills.. the earth is heating up enough to cause more volcanoes to erupt which view co2 ( approximately on an average of 15 parts per million) and among other things sulfur something or another which when it is in the atmosphere reflects the sun rays or heat which helps cool the earth. at some point if all this co2 does cause extra heating over and above the normal cycles of the earth… what the earth just make more volcanoes and more toxic fumes and dust and particles until it just annihilates the human race !? I read some articles yesterday that Greenland, Swiss Alps and Alaska all have green plants that have been frozen under all that ice sometime in the past which means they were all uncovered by ice at one time. as this article speaks about other than all of mammals choking to death… are we not still coming out of an ice age? I feel when the last woolly mammoth is recovered from the Glaciers And the plants in the Andes that have flowers on them underneath the eyes are revealed and get the grow to where they were… we have at least another 200 to a thousand years of retreatforest how about it.

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    You need to consider the long-term effects from chronic atmospheric exposure. That is the place where the conversation should begin. Forget the perspectives about short term exposure (e.g. the information from the EPA), because the main concern with atmospheric CO2 toxicity is related to chronic exposure. No one has done this long term research, so no one can say for sure what the consequences are. CO2 is physiological waste that induces numerous side effects on your cells. Scientists need to evaluate the effects of long term exposure to ambient CO2. My opinion is that human civilization has been very naive to fill the atmosphere with CO2 via fossil fuel combustion, because NO ONE has done the work to understand the long term chronic effects. Not being funny, but imagine if you had to put a milliliter of your urine into every glass of water that you drank. And you had to do this everyday. I don’t think it takes a genius to realize that chronic exposure to atmospheric CO2 levels that are at a 15 million year optimum is probably affecting our health in a negative manner. Once again, no one has done the research to understand the mechanism better. This is a huge gap.

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    F Face


    Absolutely no one, other than idiots like yourself, has ever suggested that the increases in CO2 concentrations could be toxic

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      [quote name=”F Face”]Absolutely no one, other than idiots like yourself, has ever suggested that the increases in CO2 concentrations could be toxic[/quote]

      Maybe you should look at this article, and then you can start to understand the possibility. Most people don’t realize that CO2 is a highly toxic substance that has associated (along with CH4 and NO) during the five mass extinctions of the past. The key question isn’t whether CO2 is toxic to humans (or plants and animals in general) but rather if the rate of change in atmospheric CO2 is toxic.

      Here’s the article that you should read in order to start to understand the implications. It goes deep into the physiology, which is all the more reason why we need better integration between the atmospheric science community and medical community.

      Article, “NF-kB Links CO2 to Innate Immunity and Inflammation in Mammalian Cells.”

      Link to article:

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