Atmospheric Composition

Understanding Atmospheric Composition is both simple and handy in understanding how mankind can influence climate. Many people think the atmosphere is just too big for humans to influence? It sounds like a reasonable statement, until you realize that you don't need to change the whole atmosphere to change climate... you just need to change a little bit of it.

Atmospheric Compostion

With no understanding of the atmosphere and it's composition, it is easy to see why someone might question how we could change the climate. The atmosphere is really big. But to get this in perspective, you really only need to know how much of the atmosphere keeps us warm.

Generally speaking, looking at the pre-industrial atmosphere, if you don't consider water vapor (a larger variable gas), the atmosphere is about 78% Nitrogen and 21% Oxygen. So, 99% of the atmosphere is accounted for in those two gases. The last one percent includes various trace gases, some are greenhouse gases, and some are not.

To get that in perspective, think about it like this. the natural greenhouse gases are CO₂, H₂O, CH₄, and N₂O. These gases comprise less than 300ths of a percent of our pre-industrial atmosphere. Then of course add water and stir :)

If it were not for that tiny fraction of greenhouse gases, in our atmosphere, Earth would be a giant frozen ball in space. It's as simple as that.

Once you understand that you don't need to change the whole atmosphere but rather you need only change a tiny fraction to change the climate or climate forcing... It becomes much easier to understand how industrial emissions can have an impact on the climate of the planet. Keep in mind that our pre-industrial atmosphere only needed, other than H₂O approximately 300^th's of a percent of the atmosphere to contain GHG's in order to keep Earth relatively warm. Changing CO2 concentration from 280ppm to approximate 400ppm is a significant increase. Now, other than H2O, nearly 400th's of a percent of our atmosphere contains greenhouse gases. Of all the GHG's CO2 is a more significant component because of it's atmospheric lifetime and the associated warming ability that goes along with this particular gas, which changes the amount of heat energy trapped within our climate system.

Table 7a-1: Average estimated composition of the atmosphere up to an altitude of 25 km (*+/- 0.5%).

Gas Name	Chemical Formula	Percent Volume	**ppm
Nitrogen	N₂	78.084%	780,840 ppm
Oxygen	O₂	20.95%	209,500 ppm
Argon	Ar	0.93%	9,300 ppm
*Water	H₂O	2.5%	25,000 ppm
*Carbon Dioxide	CO₂	0.0397%	(Dec. 12, 2014 mean est.) 399 ppm
Neon	Ne	0.0018%	18 ppm
Helium	He	0.000524%	5.24 ppm
*Methane	CH₄	0.000179%	1.79 ppm
Krypton	(Kr)	0.000114%	1.14 ppm
Hydrogen	H₂	0.000055%	0.55 ppm
*Nitrous Oxide	N₂O	0.0000325%	0.325 ppm
Carbon Monoxide	CO	0.00001%	0.1 ppm
Xenon	Xe	0.000009%	0.09 ppm
*Ozone	O₃	0.000007%	0.07 ppm
Nitrous Dioxide	NO₂	0.000002%	0.02 ppm
Iodine	I₂	0.000001%	0.01 ppm
Ammonia	NH₃	trace	trace