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400 Parts Per Million

By Bruce Barbour - May 2019

Alan Jones and other deniers often asks the question "how can carbon dioxide which is only 400ppm of the atmosphere have any affect on the climate of the planet?". His opinion of course is that it doesn't. His argument for this is based solely on his and other deniers' gut feeling - "the planet is so big and the amount of carbon dioxide so small". There is no science to back up their combined guts.

The question I would ask is - is 400 ppm really so insignificant? - in the atmosphere and in other situations.

On this page which has the heading "Climate Change Deniers", I argued that even though the concentration of carbon dioxide seems small it is not insignificant because the atmosphere is quite large. 400 ppm of carbon dioxide would equate to a layer thickness of 3.1 metres if all of the carbon dioxide was concentrated into one layer rather than spread out over the complete height of the atmosphere, and that human activity has increased that effective CO2 layer thickness by at least 0.9 metres from pre-industrial times.

As this argument is not sufficient for the deniers perhaps another argument will assist. Consider a typical aspirin tablet that can be bought in any supermarket or chemist in Australia. That has a dosage of 300 milligrams (mg) or 0.3 of a gram. (Low dose aspirin has a dosage of 100 mg.) Now take the situation that this dosage is taken by a person who, for the sake of convenience of calculation, weighs 100 kg. The question is what is this 300 mg (0.3 gram) aspirin dosage in ppm (in this case mass/mass) of the mass of person.

Number of grams in 100 kg person = 100 kg x 1000 = 100,000 gm.

So 0.3 gm / 100,000 gm. In terms of ppm = 3/1,000,000 = 3 ppm.

An aspirin which is only 3 ppm of a person's weight can have an impact on their head ache. 2 tablets, typically the recommended dosage, at 6 ppm has a bigger effect. According the arguments of the deniers this could not be. How could such a small tablet have an effect on such a large body as a person?

What would the impact be if the person took a dosage of 400 ppm at one time - that would equate to 133 standard aspirin tablets. I am not a doctor but I am guessing that the person would be in hospital getting their stomach pumped, if not dead before they could get to hospital. 400 ppm can be really really significant.

(I was going to write this article using the dosage of arsenic or cyanide necessary to kill a person, but I did not know what that dosage was and I was not prepared to Google it. I did not want that search in my search record. I think I am getting more paranoid as I get older. I am sure a similar calculation to the above could be done for the active ingredients of most medicines, many with a lot lower dosage. And yet they are still mostly effective.)

I am not trying to argue that because small dose aspirin is effective therefore small concentrations of carbon dioxide is impactful as well. That would be as silly an argument as that of the deniers. The efficacy of small doses of aspirin and other medicines tells us nothing about the impact of increasing carbon dioxide in the atmosphere. For information on that we have to rely on science and science alone. I wrote this because I am sick and tired of deniers telling people that because the relative concentration of carbon dioxide in the atmosphere is small it can have no impact. I hope my aspirin argument destroys that as a creditable hypothesis (not that it ever was). The deniers deny science and therefore have no credibility. Their statements, and ultimately they, should be treated with the contempt they deserve.

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