Guest essay by Andy May
The Earth’s atmosphere is 78% nitrogen, 21% oxygen and 0.9% argon. These are not greenhouse gases and they total 99.9%, leaving little space for the greenhouse gases methane, carbon dioxide and water vapor. The amount of water vapor in the atmosphere varies a lot with altitude and temperature. At low altitude and high temperatures (greater than 30°C or 86°F), over the ocean, it can reach 4.3% or more of the atmosphere and is less dense than dry air, causing it to rise. It will rise until the temperature is low enough for it to condense to a liquid or solid state and form clouds, rain or snow.
The amount of water vapor in the air drops to very close to zero when temperatures are below 0°C. Thus, the average volume of water vapor in the total atmosphere is very low, roughly 0.001% according to the…
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