AIR!Earth’s atmosphere recently crossed 400 ppm CO2 for the first time in millions of years and prob

AIR!Earth’s atmosphere recently crossed 400 ppm CO2 for the first time in millions of years and probably will not go back below that amount during any of our lifetimes. (http://tinyurl.com/bus4xpt). But did you know there’s something else changing in the atmosphere to go along with that CO2 rise?It’s pictured in this graph. This gas is going down, decreasing in the atmosphere as CO2 goes up. That gas? Oxygen. Oxygen in the atmosphere is decreasing.Be honest…did you just stop and take a deep breath? It really is kinda creepy to realize that the gas everyone is taught as a kid they need to survive is going down in the atmosphere.Anyway, why is oxygen going down? The same reason that carbon is going up; burning of fossil fuels. When you burn coal or gas, you’re taking carbon and turning it into CO2, and occasionally some amount of H2O. These reactions need a source of oxygen to happen, and they get that oxygen from the atmosphere. Every time a gasoline engine is run or a power plant burns coal, it consumes the same gas that animal life uses to keep itself alive. In fact, oxygen is so much of a mirror for CO2 that the yearly cycles from the growth of plants in the northern hemisphere summer shows up on this graph as well.There’s some good news though; the change in atmospheric oxygen is really small. I have to do a unit switch here…400 ppm of CO2 is equal to 0.04% CO2 in the atmosphere, while the atmosphere is over 20% oxygen. So, the decrease in oxygen is in effect a rounding error. It’s the change from 20.9% oxygen to 20.8% oxygen, give or take. Hopefully that helps everyone breathe a little easier.Beyond just freaking people out by making them think we’re running out of air, there’s some cool science demonstrated here. First, the measurement of decreasing oxygen hasn’t been done for as long as the measurement of increasing CO2 because of the abundances of the gases. The change in atmospheric oxygen is a very tiny change in a big number, and those types of numbers are hard to measure precisely. It took until the 1990’s to really get an accurate measure of atmospheric oxygen.Conversely, with CO2, researchers are measuring big changes in small numbers. Since those are easy to measure, that measurement has been done since 1960. It’s a lot easier to measure a 40% increase in atmospheric CO2 than it is to measure a 0.1% decrease in atmospheric oxygen. That’s actually why the units on this graph are so funky; “per meg” units are 1000 times smaller than “Per mille” units and 10000 smaller than “per cent” units.Another interesting point; the decrease in oxygen content is actually quite a bit larger (on an absolute basis) than the increase in CO2. This makes sense too; not all of the CO2 released by man has gone into the atmosphere; about half has been taken up by the oceans. That burned carbon still removes oxygen from the atmosphere even if the CO2 molecule doesn’t immediately wind up in the atmosphere. Also, water vapor is produced by burning of hydrocarbons; the production of water removes oxygen from the atmosphere as well. Altogether, we’ve removed roughly 3 molecules of oxygen from the atmosphere for every 1 molecule of CO2 that has been generated by fossil fuel burning.Finally, it’s worth noting what else this graph says. Occasionally people hypothesize that the source of the carbon in the atmosphere is something other than man’s burning of fossil fuels, something like volcanic emissions. Volcanoes do emit CO2, but they emit quite a bit less than man has through fossil fuel use, and that shows up in this plot. Volcanic CO2 emissions don’t remove oxygen from the atmosphere; the CO2 comes out of volcanoes already made as CO2. This plot is one of the fingerprints of fossil fuel use; burning fossil fuels doesn’t just emit CO2, it also takes oxygen with it, and no other source of CO2 does both.-JBBImage source: UCSD and the Keeling Curvehttp://explorations.ucsd.edu/files/Features/Keeling_Curve/page4.phpDiscussion with Dr. Keeling:http://blogcritics.org/scitech/article/atmospheric-oxygen-levels-fall-as-carbon/ -- source link

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