Space/Science — HabitableZone

Space/Science » in reply to re: The actual numbers, like anybody cares.

continuing
gbaikie — (archived)

"So why aren't climate scientists a lot more worried about water vapour than about CO2? The answer has to do with how long greenhouse gases persist in the atmosphere. For water, the average is just a few days."

But climate scientist are *worried* about water vapor- most of their projected increases in global temperature are due from expectation that "forcing affects" due to increase level of CO2 which are suppose to increase average temperatures will cause an increase level of global water vapor.

And another thing is that a lot of water vapor does stay around for a very long time. Cold antarctic air is very dry- but if want measure water vapor in ppm like you do CO2
then there is some water vapor in that very cold, very dry air.

Now, on this water planet it rains a lot. But say, you select a non water planet like Mars. On that deep freeze of a planet
Mars' atmosphere has "0.03% Water vapor"
http://en.wikipedia.org/wiki/Mars

Or another way to say this is water vapor on Mars is about 300 ppm. Which btw is slightly less ppm of water vapor on Mars than we have ppm of CO2 on Earth.
Merely from the fact that there are such tiny amount of water vapor on Mars- it's a fair guess to say that water vapor [of terms of the percentage of total volume] stays in the Mars atmosphere much longer than compared to Earth. But this is only because Earth is constant dumping HUGE amount of water in the form of rain- and the water vapor that "remains" in the atmosphere is small in comparison.

Now finally the idea that CO2 persist in the atmosphere for a long time is utter rubbish. CO2 has an average life of about a decade. And since the H2O molecule of vapor isn't chemically altered [such as it rains and then evaporate] if count CO2 in the same manner- where CO2 goes in and out of the ocean, gets absorbed by rain, etc, etc then it's average life in the atmosphere could be closer to a year or so, perhaps far less.

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