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Is the amount of oxygen in the atmosphere decreasing?

Is the amount of oxygen in the atmosphere decreasing (due to industrial gas usage in steel-making say) which is in turn increasing the proportion of CO2 in the atmosphere, rather than simply CO2 production from burning fossil fuels?
Andrea from West Yorkshire (age 35-44)

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3 Responses

  1. This is an interesting question and the short answer is yes the level of oxygen in the atmosphere is decreasing by a small amount due to the burning of fossil fuels. However, the amount of decrease is very small and doesn’t pose a risk to life. Also, because the rate of change is so small, measuring it poses a challenge to scientists.

    The present global atmospheric oxygen content is approximately 21 volume %, or 210,000 ppm by volume, with a small decreasing trend of 4ppm per year. This is a very small rate of decrease. To change the oxygen content of the atmosphere from 210,000 ppm to 209,000 ppm (21 to 20.9%), would require 250 years at the present rate of oxygen consumption.

    The decrease is due to the burning of fossil fuels and can be represented by the reaction:

    CH(x) + (1 + 1/4x)O2 = CO2 + 1/2xH2O

    where CH(x) represents the average composition of fossil fuels.

    Since the late Palaeozoic (350-400 million years ago) the concentration of oxygen in the atmosphere has been closely regulated within the bounds of approximately 18-25% by feedbacks involving organic processes. Indeed, today, whilst burning fossil fuels we see evidence of a feedback process that results in a rate of oxygen depletion that is slower than that expected from the known inventory of fossil fuel burning.

    Increased photosynthesis, at elevated CO2 levels, is resulting in ‘new’ production of oxygen and uptake of CO2.

  2. It has been suggested that most cities have less oxygen than the trademark 20%, with some as low as 10%. Also, the 20% figure comes from dry air measurements. With the presence of humidity the percentages move around a bit.

  3. I am also not convinced that oxygen generation will continue with the increase in sprawl and destruction of oceanic habitats. We may eventually find ourselves in quite a bit of trouble. Although this will likely not occur untill our grandchildrens’ time.

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