# Water vapour
**URL:** https://boards.straightdope.com/t/water-vapour/498065
**Category:** Factual Questions
**Created:** [May 29, 2009, 6:55pm UTC](https://boards.straightdope.com/t/water-vapour/498065 "2009-05-29T18:55:43Z")
**Posts on this page:** 17
**Page:** 1
### Author:  [@Kabob\_07](https://boards.straightdope.com/u/Kabob_07)
#### Post date: [May 29, 2009, 6:55pm UTC](https://boards.straightdope.com/t/water-vapour/498065/1 "2009-05-29T18:55:43Z")
I am a student in high school and i am trying to create a power point for a skeptic argument on how water vapour is greatly affecting our climate. But, i am struggling to think of information to put into the show. I dont know what to talk about. Any ideas would be extremly appreciated.
Thank you.
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### Author:  [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)
#### Post date: [May 29, 2009, 7:31pm UTC](https://boards.straightdope.com/t/water-vapour/498065/2 "2009-05-29T19:31:38Z")
Which side are you taking? I don’t see that water vapor in and of itself has a strong effect on the climate. It is, after all, self correcting. The atmosphere will only hold the water it can hold, and everything else will precipitate. There may be a small effect, but that is likely caused by higher temperatures raising the amount of water the atmosphere holds.
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### Author:  [@Kabob\_07](https://boards.straightdope.com/u/Kabob_07)
#### Post date: [May 30, 2009, 12:17am UTC](https://boards.straightdope.com/t/water-vapour/498065/3 "2009-05-30T00:17:35Z")
I am taking the side that is stating that Water vapor has a definite affect on climate change and the warming of our planet
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [May 30, 2009, 12:52am UTC](https://boards.straightdope.com/t/water-vapour/498065/4 "2009-05-30T00:52:00Z")
And what do you have to back that up? If nothing, why did you choose that stance?
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [May 30, 2009, 12:52am UTC](https://boards.straightdope.com/t/water-vapour/498065/5 "2009-05-30T00:52:52Z")
It does not. Water vapor IS a powerful greenhouse gas, but it’s necessarily present in the atmosphere simply because the surface of the planet is covered with liquid water and the stuff evaporates. And it’s self-limiting as to the amount the air can contain.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [May 30, 2009, 2:17am UTC](https://boards.straightdope.com/t/water-vapour/498065/6 "2009-05-30T02:17:50Z")
[Evaporation from Water Surfaces](http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html)
> [@](#):
>
> **The amount of evaporated water from a water surfaces - like swimming pools or an open tanks - depends on the temperature in the water and in the air, and the humidity and velocity of the air above the surface - online calculator**
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### Author:  [@Napier](https://boards.straightdope.com/u/Napier)
#### Post date: [May 30, 2009, 4:01am UTC](https://boards.straightdope.com/t/water-vapour/498065/7 "2009-05-30T04:01:33Z")
Lighten up, guys, I think Kabob is onto something. Water is a greenhouse gas, as QED says. Moreover, it contributes positive feedback because the more water vapor there is in the atmosphere, the warmer the atmosphere becomes, which increases the amount of water vapor it can hold. I think this is believed the main reason Earth alternated so violently in its early history - IIRC it appears the average temperature on Earth once increased by 120 Fahrenheit degrees in just 100 years (hope I got the numbers right, read this somewhere, maybe one of those Best American Science and Nature Writing collections).
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### Author:  [@WarmNPrickly](https://boards.straightdope.com/u/WarmNPrickly)
#### Post date: [May 30, 2009, 11:50am UTC](https://boards.straightdope.com/t/water-vapour/498065/8 "2009-05-30T11:50:06Z")
It is still disengenuinous to make a case that one greenhouse gas warms the earth but another doesn’t. The physics is identical for both of them. The only difference is when the concentration of water gets to high, it rains.
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### Author:  [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)
#### Post date: [May 30, 2009, 2:50pm UTC](https://boards.straightdope.com/t/water-vapour/498065/9 "2009-05-30T14:50:50Z")
> [@WarmNPrickly](#):
>
> It is still disengenuinous to make a case that one greenhouse gas warms the earth but another doesn’t. The physics is identical for both of them. The only difference is when the concentration of water gets to high, it rains.
Has anyone ever made the case that water vapor doesn’t warm the earth?
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [May 30, 2009, 3:17pm UTC](https://boards.straightdope.com/t/water-vapour/498065/10 "2009-05-30T15:17:35Z")
> [@Bill\_Door](#):
>
> Has anyone ever made the case that water vapor doesn’t warm the earth?
Once, for twenty minutes, in the sixties.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [May 30, 2009, 3:24pm UTC](https://boards.straightdope.com/t/water-vapour/498065/11 "2009-05-30T15:24:47Z")
Nowadays, lots of people seem to miss the point that the increase in water vaporization with increasing temperature serves to amplify the temperature effect produced by other gases.
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### Author:  [@mangeorge](https://boards.straightdope.com/u/mangeorge)
#### Post date: [May 30, 2009, 3:39pm UTC](https://boards.straightdope.com/t/water-vapour/498065/12 "2009-05-30T15:39:47Z")
I haven’t thought this through, but what about the _lack_ of water vapor. As in Death Valley, California? Arid, treeless areas don’t do much to remove CO[sub]2[/sub] from the air.
We are talking about humidity, right?
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### Author:  [@mangeorge](https://boards.straightdope.com/u/mangeorge)
#### Post date: [May 30, 2009, 3:54pm UTC](https://boards.straightdope.com/t/water-vapour/498065/13 "2009-05-30T15:54:49Z")
> [@Kabob\_07](#):
>
> I am taking the side that is stating that Water vapor has a definite affect on climate change and the warming of our planet
FYI; “effect” is generally a noun, and “affect” is generally a verb. I usually have to pause a moment when I use one or the other. 😉
BTW; was this subject assigned to you, or did you, uh, think it up?
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### Author:  [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)
#### Post date: [May 30, 2009, 4:12pm UTC](https://boards.straightdope.com/t/water-vapour/498065/14 "2009-05-30T16:12:06Z")
> [@Squink](#):
>
> Nowadays, lots of people seem to miss the point that the increase in water vaporization with increasing temperature serves to amplify the temperature effect produced by other gases.
That guy up in [post 2](http://boards.straightdope.com/sdmb/showpost.php?p=11191349&postcount=2) didn’t.
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### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [May 30, 2009, 4:44pm UTC](https://boards.straightdope.com/t/water-vapour/498065/15 "2009-05-30T16:44:22Z")
> [@Bill\_Door](#):
>
> That guy up in [post 2](http://boards.straightdope.com/sdmb/showpost.php?p=11191349&postcount=2) didn’t.
Just think of water/vapor as a transistor in a circuit. When you add another gas that increases the temp, that increase drives water into the vapor phase. That vapor _also_ increases the temp, i.e. the gain is \> 1.
Now **mangeorge** ’s plants require water/humidity, and suck up CO[sub]2[/sub], but that’s a secondary effect.
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### Author:  [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)
#### Post date: [May 31, 2009, 2:12am UTC](https://boards.straightdope.com/t/water-vapour/498065/16 "2009-05-31T02:12:02Z")
Water vapor is related to cloud cover, which may have a cooling effect on the earth. Cloud cover then leads to rain, which may encourage plant growth and extract co2 from the air.
In climate science, nothing is simple.
P.S., kabob, why is yours the “skeptical” side?
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### Author:  [@matt](https://boards.straightdope.com/u/matt)
#### Post date: [May 31, 2009, 11:34am UTC](https://boards.straightdope.com/t/water-vapour/498065/17 "2009-05-31T11:34:37Z")
> [@Bill\_Door](#):
>
> Which side are you taking? I don’t see that water vapor in and of itself has a strong effect on the climate. It is, after all, self correcting. The atmosphere will only hold the water it can hold, and everything else will precipitate. There may be a small effect, but that is likely caused by higher temperatures raising the amount of water the atmosphere holds.
Except that the atmosphere as a whole is nowhere near saturated - in the vast majority of areas, humidity is far below 100%.
Most climate models assume that with global warming, the _relative_ humidity will remain fixed, which means the actual water vapour content (in mass per unit volume) of the atmosphere will increase with increased temperature. This would increase the water-vapour greenhouse effect, amplifying the carbon dioxide greenhouse effect.
However, there is also the possibility that increased temperatures affect cloud cover so as to reflect more heat into space, providing a negative feedback. See for example Miller’s 1995 paper, [http://ams.allenpress.com/archive/1520-0442/10/3/pdf/i1520-0442-10-3-409.pdf](http://ams.allenpress.com/archive/1520-0442/10/3/pdf/i1520-0442-10-3-409.pdf), Sud et. al. [http://adsabs.harvard.edu/abs/1999GeoRL..26.1019S](http://adsabs.harvard.edu/abs/1999GeoRL..26.1019S), or more recently Spencer et. al. [http://www.drroyspencer.com/Spencer\_07GRL.pdf](http://www.drroyspencer.com/Spencer_07GRL.pdf).
Roy Spencer is one of the few AGW critics who is qualified in meteorology and gets his research published, so his website would probably be useful to you. Try here for a primer on his arguments:
[http://www.drroyspencer.com/2009/05/a-layman’s-explanation-of-why-global-warming-predictions-by-climate-models-are-wrong/](http://www.drroyspencer.com/2009/05/a-layman%E2%80%99s-explanation-of-why-global-warming-predictions-by-climate-models-are-wrong/)
He also happens to be a creationist of sorts, which doesn’t do a lot for his scientific credibility IMO, but there is at least _some_ research published in the scientfic press indicating negative feedbacks from water vapour. Google “iris effect” and “clouds negative feedback” for more.