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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 Composition

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, 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 300th'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%

397 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

* considered relatively variable gases

** parts per million

Atmospheric Composition Change: July 09, 2011

Network for the Detection of Atmospheric Composition Change (NDACC) http://www.ndsc.ncep.noaa.gov/

 

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