global warming question

[jbm]

My sister is a high school teacher and she was asked a question for which she has been unable to find a definitive answer. If Carbon dioxide levels are increasing, are there any studies available to show that oxygen levels are decreasing? If more and more oxygen is being bound to carbon in the formation of excess carbon dioxide, it would seem that oxygen would be decreasing unless some other reaction is taking place which is replacing the oxygen bound in the CO2.

My sister suspects that her student is being used by a "global warming doubter" who also teachs at her school. The other teacher was very negative when my sister showed An Inconvenient Truth to her classes.

[WindRavenX]

1. I'm a little confused at the question...

let me restate the question to see if I get it:

the student is asking why there doesn't seem to be a decrease in O2 despite a rise in CO2?

[HiFructosePronSyrup]

2. That's a good question.

I was wondering it myself the other day. Haven't got any answers.

The level of O2 in the atmosphere's about 21%. Whereas CO2 is less than one tenth of one percent. Global CO2 levels have increased by ~33% since the industrial revolution, so if the level of O2 has changed then it'd be trivial in comparison to the change in CO2.

[Sal Minella]

3. I keep wondering about this too. If we're pulling all those carbon atoms out of the ground

(coal and gas and oil) and spewing each one into the atmosphere attached to two oxygen molecules, are we eventually going to run out of oxygen molecules? Have been hoping somebody would reassure me on this.

I vividly remember the high-school chem experiment when the teacher "pours" the heavier carbon dioxide gas into the folded paper trough and the gas runs down the trough onto the candle flame and snuffs it out.........

[mike_c]

4. no, oxygen levels are NOT decreasing....

In fact, there is a slight possibility that increased CO₂ might slightly increase atmospheric O₂ by increasing photosnythesis, but that's probably not very likely because the gains in photosynthetic efficiency will likely be offset by increased heat stress.

But anyway, back to your question-- what's happening is that more and more CO₂ is being added to the atmosphere. In practice, this means that atmospheric gas density is increasing, but since we're only talking about increases in the parts per million range the actual gas density isn't changing much at all. The primary effect is on heat storage.

--on edit: Oh, I think I misunderstood your question-- did you mean because of the oxygen reacting with carbon to oxidize it to CO₂? That's a miniscule amount of oxygen, actually, relative to the amount in the atmosphere, and it's easily made up for by photosynthesis.

[WindRavenX]

7. ah--I thought it might have something to do w/ photosynthetic increase

thx for the response

[jpak]

5. The answer is yes, but these measurements are extremely difficult to make...

...as the reduction in atmospheric oxygen due to fossil fuel combustion is vanishingly small compared to the (huge) mass of oxygen in the atmosphere.

Researchers get around this by determining precise changes in the ratio of oxygen to nitrogen in the atmosphere...

What Atmospheric Oxygen Measurements Can Tell Us About the Global Carbon Cycle (1993) Keeling, R. F. et al., Global Biogeochemical Cycles, Vol. 7, pp. 37-67

The ratio of O:N is declining...and it's due to combustion of fossil fuels.

We will not suffocate, however, as the amount of fossil fuel carbon in the Earth's crust could not significantly reduce atmospheric oxygen levels - even if we burned it all.

edit: some "light reading" on the subject...

http://www.nature.com/nature/journal/v426/n6964/full/nature02131.html

http://www.nature.com/nature/journal/v381/n6579/abs/381218a0.html

[hobbit709]

6. CO2 levels have risen

from about 280 parts per million in 1800 to about 380 parts per million in 2000. There has been a corresponding decrease in O2. It is a neglible decrease in terms of the 21% O2 content of the atmosphere.

[jbm]

8. Thanks to all that responded!

I had to leave unexpectedly so I wasn't able to stay with the thread, but I will pass your responses on to my sister. Thanks for all of your help!