Almost all (99 percent) of Earth's atmosphere consists of two main gases: nitrogen (about 78 percent) and oxygen (21 percent by volume). These gases are important in a number of ways. Oxygen, of course, is vital to the respiration of humans and animals. Both gases play roles in the numerous complex biogeochemical cycles that support life on the planet, but they play almost no direct role in regulating the climate.

The remaining one- percent or so of Earth's atmosphere is made of small amounts of a number of "trace" gases. One of the most abundant of these is argon, which for climate purposes can also be ignored. Other trace gases include water vapour, carbon dioxide, nitrous oxide, methane, chlorofluorocarbons (CFC's), and ozone - all of which can be important in the regulation of climate.

Earth's atmosphere is big, indeed it's staggering (Its mass is estimated at 5,600,000,000,000,000 ton). Many people are accustomed to thinking that, because of the enormity of the atmosphere, most human air pollution just dissipates and is eventually so diluted that it becomes harmless. All human clearing and burning of forests for agriculture, and all the smoke stacks of industrial civilisation, seemingly have not changed the basic character of our nitrogen-oxygen atmosphere. As tempting as it is to think this way, it can be a big mistake when it comes to climate change.

In fact, it is the trace gases that are most important. Precisely because their amounts in the atmosphere are so small, pollution and other forces resulting from human activities can alter the proportions of atmospheric trace gases in quite significant ways.

Related Articles:

- Gases Introduction
- Carbon Dioxide
- Halocarbons
- Methane
- Nitrous Oxide
- Ozone
- Water Vapour