How much Greenhouse Gas is in the Atmosphere?

The following graph shows the proportions of atmospheric gases as reported by NASA.  The vast majority of the atmosphere is Nitrogen and Oxygen, which account for about 99% of the atmosphere.  Of the remaining 1% (the expanded pie slice on the right), almost all of it is Argon (0.93%).  The tiny red slice is Carbon Dioxide, which accounts for 0.035% of the Earth's atmosphere.  On days with normal or higher humidity, water is the third largest component gas in the atmosphere.  Water vapor is a powerful greenhouse gas , but water vapor's concentration in the atmosphere is highly variable. Of all the greenhouse gases,water vapor has the largest impact on global temperature because of its relatively high concentration in the atmosphere, far outstripping the effects of methane and Carbon Dioxide combined (water vapor accounts for 2/3 of today's greenhouse gas warming). In fact, without the warming effect of water vapor, Earth would have an average temperature below freezing (this actually occurred at the end of the Precambrian).

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