A Window on Water Vapor and Planetary Temperature
18 06 2008
Here is some interesting news; according to data from NOAA’s Earth System Laboratory, atmospheric water vapor is on the decline globally.
You’ve probably heard many times how water vapor is actually the most important “greenhouse gas” for keeping our planet warm, with an effectiveness far greater than that of CO2.
It is generally accepted that the rank of important greenhouse gases is:
* water vapor and clouds which causes up to 70% of the greenhouse effect on Earth.
* carbon dioxide, which causes 9–26%
* methane, which causes 4–9%
* ozone, which causes 3–7%
Note the range of uncertainties, on water vapor some say the percentage goes up to 90% with reduced numbers on the other three.
It is absolutely true that water vapor is the gas most responsible for the “greenhouse effect” of our atmosphere. Greenhouse gases let short-wave solar radiation through the atmosphere, but impede the escape of long-wave radiation from the Earth’s surface. This process keeps the planet at a livable temperature: Without a suitably balanced mixture of water vapor, CO2, methane, and other gases in the atmosphere, Earth’s average surface temperature would be somewhere between -9 and -34 degrees Fahrenheit, rather than the balmy average 59 degrees it is today.
This graph then from NOAA’s Earth System Research Laboratory, showing specific humidity of the atmosphere up to the 300 millibar pressure level (about 8 miles altitude) is interesting for it’s trend:
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