[Jeff Lewis]

Jeff Lewis  asked the Naked Scientists:

Dear Chris,

Everyday I hear about the threat of global warming due to increasing levels of carbon dioxide.

I never hear anything about oxygen levels. If CO2 is going up, oxygen levels must be going down and that seems more worrying to me.

In my school days in the 1960s oxygen was about 20% of the volume of air. What is it now? And at what level do humans start to be adversely affected?

Presumably the stronger humans will adapt like high-altitude Peruvians. Could you discuss other effects of low oxygen on our planet please ?

Best wishes
Jeff Lewis from Sutton, Cambridgeshire


What do you think?

[JimBob]

Yes - oxygen levels have fallen and risen over geologic time and this can be measured by isotope variations on carbon for the last 50,000 years or so and by other methods for the longer geologic time.

At present the answer is a definite YES The first reference I found  is :

http://www.climateark.org/articles/1999/atoxfall.htm


I have read in "Science" that more recent studies also corroborate this finding.

[crandles]

>oxygen levels must be going down and that seems more worrying to me.

Simple answer - No.

If we increased CO2 by a factor of 10 from 387ppm to 3870ppm through burning carbon to make CO2 the the oxygen level would be going down from 20.95% to 20.6%. That is a huge change in the CO2 level but the O2 change is managable - you can get a much bigger effect on oxygen available by climbing a mountain. The CO2 would reach toxic levels before the O2 reduction became a problem. Global warming is more likely to become a problem before toxic CO2 levels are reached.