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Topics - Pragma

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Science / Water vapour and warming potential
« on: July 02, 2019, 05:05:08 AM »
I have been trying to get a number for the relative warming potential of water vapour and it seems elusive.

More than that, there seems to be some possible deception going on.

I have been told that H2O is a more powerful GHG but, IIRC, in Wikipedia, under GHGs, they state that H2O is not included because it is not persistent.

I think this is a rubbish statement. Methane is also not  persistent, but on a longer timeframe. Same for CO2.

Here is my reasoning.

At a given average earth temperature, there will be x amount of water vapour keeping the earth warm. The next day it may be some totally different water vapour doing the same job.

If the level of water vapour increases 7%/deg C, and we have raised the earth's temperature by one degree C, then on average, we now have 7% more water vapour in the air at any time, and whatever effect the water vapour had, it is now 7% more, regardless of how persistent it is.

I would like to know what the CO2 equivalent of the increased water vapour is, as it is cited as a large component in a runaway warming scenario.

Am I missing something that cancels this out, or is it a pesky little detail that no one wants to talk about? Why is methane and NO used to calculate a total CO2 equivalent, but water vapour is not?

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