Breathe, breathe in the air...

December 14, 2007 11:25 AM

Not to start a fight but I am curious about this one...If the entire atmosphere is 100% and nitrogen is 89% and the inert gases are 0.9% and the rest is the O2 we breathe and more and more CO2 is being made [carbon burning made that is] from that O2 and not going back out of the system as released O2 will we see a drop in the amount of O2 we have to breathe? Does the actual % of the various gases get checked on by anyone? And would we see it first decline at higher altitudes or in the deaths of animals who need more O2 for their specific needs..........which ones are the mine canaries here?
posted by Freedomboy to Science & Nature (12 answers total)

nitrogen is 77-78%
posted by bruce at 11:33 AM on December 14, 2007

CO2 exists at about 380 parts per million, at the moment. O2 exists at about 209000 parts per million.

Therefore, a one percent conversion of oxygen to CO2 would boost CO2 abundance by a factor of about five or six. This would make Earth uninhabitable in short order, I believe. A percent of oxygen should be survivable by most organisms, so loss of it is not going to be, in itself, a problem.
posted by topynate at 11:35 AM on December 14, 2007

Nitrogen is 78%, not 89%. CO₂ is around 0.04%, so even increasing it by a factor of ten would have an imperceptible impact on the oxygen content.

Does the actual % of the various gases get checked on by anyone?

Very carefully.
posted by Mapes at 11:36 AM on December 14, 2007

Uh, the way his question is phrased is an absolute mess, but let me take a stab.

First off, you're treating percentages as totals. That is to say, carbon that is currently trapped in places other than the atmosphere (wood, coal, oil, you and me) that is later relased does not lower the amount of oxygen available, only the percentage of the atmosphere that is made of up oxygen.

FYI: According to Wikipedia, the atmosphere "contains roughly (by molar content/volume) 78% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, trace amounts of other gases, and a variable amount (average around 1%) of water vapor. "
posted by absalom at 11:36 AM on December 14, 2007

"... And would we see it first decline at higher altitudes or in the deaths of animals who need more O2 for their specific needs..........which ones are the mine canaries here?"
posted by Freedomboy to science & nature

The physiology of respiration for living things varies tremendously. Some would argue, that in acid rain, which is partly due to CO₂ being dissolved in rain water (but also and perhaps more influenced by nitrous and sulfuric emissions of fossil fuel combustion), we've already seen the first effects of rising CO₂ levels, as long ago as the late '60s. That's when people first noticed global patterns of forest die off at high altitudes that correlated with increasing acidity of rain water, and was soon seen in acidification of high mountain lakes. The "canaries" in that case, were trees and fish.
posted by paulsc at 12:05 PM on December 14, 2007

As others have pointed out, carbon dioxide is a tiny percentage of the atmosphere compared to oxygen, so even a doubling of carbon dioxide would have almost no effect on oxygen percentage. So oxygen breathing animals will not be measurably affected. On the other hand, photosynthesizing plants that "breathe" carbon dioxide are greatly affected by doubling the concentration of CO2. There are lots of scientists that are busy studying this effect, including increased growth rates of oceanic algae, invasive weeds, grasses and commercial forests. So your "canary" would more likely be a plant.
posted by JackFlash at 12:54 PM on December 14, 2007

And to add to all that people have already posted, in practice your average aerobic organism can take in oxygen at one or two percent lower or higher than what's "standard" in the atmosphere without undue problems.
posted by NucleophilicAttack at 1:19 PM on December 14, 2007

The proper way to approach the question is to look at the partial pressure of oxygen; that is what the body needs to survive, and it will not be changed by increased amounts of carbon dioxide. At high altitudes, the partial pressure of oygen is what causes hypoxia (although not other aspects of altitude sickness, such as pulmonary and cerebral edema); it can be offset by increasing the percentage of inspired oxygen. Conversely, when diving, the elevated partial pressure of oxygen can cause oxygen toxicity and can be offset by the use of gas mixtures with less oxygen. The partial pressure of oxygen that humans get breathing room air is about 102 mmHg at sea level and is calculated using the alveolar gas equation. Most people can withstand significantly less; the same equation gives a partial pressure of 35mmHg at the summit of Mt. Everest, but those who climb it without oxygen have undergone some significant altitude acclimatization.

The amount of oxygen that would have to be sequestered as CO2 to make a significant dent in the partial pressure of oxygen available is orders of magnitude greater than what is likely to happen in even the most pessimistic projections.
posted by TedW at 2:52 PM on December 14, 2007

That is to say, carbon that is currently trapped in places other than the atmosphere (wood, coal, oil, you and me) that is later relased does not lower the amount of oxygen available

That is not exactly true, since carbon combines with oxygen to form carbon dioxide; however, as has been pointed out, there is so much excess oxygen in the air compared to carbon dioxide that the effect is slight.

To answer the second part of your question, I tried googling oxygen uptake and oxygen kinetics in different species and there has been a lot of research in this area but I could not find a comprehensive review.
posted by TedW at 3:24 PM on December 14, 2007

I was startled to read a claim recently that

the Paleozoic period, about 300 million years ago, was a time of huge and abundant plant life and rather large insects -- dragonflies had two-and-a-half-foot wing spans, for example. The air's oxygen content was 35% during this period, compared to the 21% we breathe now,...

Presumably all this oxygen has disappeared due to a combination of oxidation of minerals and the actions of living things (such as the production of carbonates for coral and shells).

It's not clear to me if this decline is continuing, or how far it could go, assuming the 35% figure is correct.
posted by jamjam at 7:26 PM on December 14, 2007

Well, I think the short answer to your question is "yes," but the slightly longer answer is "it doesn't matter," at least not in the way you're thinking. CO2 emissions aren't going to cause us to die from lack of oxygen. (They may well kill us all for other reasons, but not because of "oxygen depletion" or something.)

Easiest explanation, and I offer this in addition to the ones already above: you can survive on MUCH LESS oxygen than is present in the atmosphere at sea level. I don't remember the exact number but I think it's something around 9-10% O2 before a healthy person will start blacking out (it depends on how much physical exertion you're under and what you're used to). This is why CPR works, incidentally: even after one person takes a breath in and exhales it, the air still contains enough O2 to keep another person alive.

Also, if you set aside the greenhouse effect and algae blooms, which are the real concerns regarding carbon emissions, I suspect that you'd find it hard to drive CO2 levels very high, because they'd be limited by plant growth. If you push it higher, plants grow faster, hence more CO2 -> O2 conversion; it's not a completely static system.

I'm not attempting to minimize the dangers of carbon emissions in any way here, but I think that the risk isn't that we'll run out of O2 and strangulate, it's that we'll bash the atmosphere into achieving an equilibrium state that's unpleasant (hotter, colder, more dynamic/unpredictable, whatever) compared to what it is now.
posted by Kadin2048 at 9:35 PM on December 14, 2007

The oceans are where there is likely to be a significant and deadly drop in O2. Water has lower and more variable O2 concentrations to begin with, and warm water holds less O2. Plus the pH is being driven down by the excess CO2 getting dissolved in the water. For terrestrial environments, people are still trying to figure out what's most likely to happen, but plants are what's generally thought to be the canary there. There's a bit on what's expected to be most affected by rising CO2 here. To get a sense of what low oxygen in the oceans does to the life there, you might read this and this. Note that for the Oregon dead zone, the press are eager to connect the recurring (and growing) dead zone off Oregon's coast to global warming, while the scientists aren't yet certain that it is the cause for the changes. But they definitely suspect it is and are looking into it.
posted by Tehanu at 12:15 AM on December 23, 2007