I second this.
Edit - oh, I didn't reply about the whole hydrogen power thing - when I was talking about the greenhouse potential of water, it was that it could become a major issue if the amount in the atmosphere changes massively (which would happen if you got a big increase in hydrogen cars), which is pretty much what that NS article you linked to said
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 9:43, archived)

No it doesn't.
It specifically says "This rapid turnover means that even if human activity was directly adding or removing significant amounts of water vapour (it isn't), there would be no slow build-up of water vapour as is happening with CO₂"
( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 9:49, archived)

Got the link again?
could have sworn it said that while water maintians a short atmospheric cycle, a significant change in emissions could still have major effect on climate...

Edit - I think it's symantics - It won't build up like CO2 because it's atmosnpheric period is only days, but major man-made emmissions could alter the equilibrium between atmospere and surface water, which could still have a major effect on climate.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 9:53, archived)

Other way around.
If the temperature increases (because of other greenhouse gases) then the amount of water in the atmosphere will increase. THE SEAS WILL BOIL.

Howd up a sec ...

environment.newscientist.com/channel/earth/climate-change/dn11652

edit: that's definitely not semantics ... it's an effect of global warning, not a cause. That's a pretty clear and important distinction. The steam that comes from hydrogen fuel cells is not a contributer to global warning, which is what the myth asserts.
( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 9:55, archived)

have you chaps heard of the seawater greenhouse?
it made for interesting reading
www.seawatergreenhouse.com/
(Dangermouse., Wed 27 Aug 2008, 9:58, archived)

If that works, that would be quite cool.

( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 10:01, archived)

Oooh.

( Newington, Wed 27 Aug 2008, 10:04, archived)

Shit, that's so obvious
why didn't I think of that? innovative cunts.

I'll just stick my grump in by pointing out that they are re-introducing seawater into the sea at a much higher salinity, so any major exploitation of the technology would render areas of the sea biologically dead on a localised basis ;)
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 10:09, archived)

Do they have to put the runoff back into the sea?

( Newington, Wed 27 Aug 2008, 10:11, archived)

not strictly, I suppose
but what else are you going to do with it, particularly if it's exploited on a large scale?
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 10:12, archived)

Sell it to Glasgow to put on their fish suppers.

( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 10:14, archived)

genius.
the concept is complete. we've done it.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 10:29, archived)

Not loading right now ...
yeah, it's all about equilibrium. I'd still maintain that major water constant emissions would effect the atmosphere/surface equilibrium but I take your point about short life in the atmosphere. But since water vapour will rise with temp anyway, we're pretty much toast regardless.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 10:01, archived)

Really soggy toast.
Yurk.
( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 10:02, archived)

It doesn't seem to.
environment.newscientist.com/channel/earth/climate-change/dn11652
It mentions that the effect of water vapour in the atmosphere will be significant when there is more water vapour in the atmosphere because of rising temperatures, but it doesn't mention water emissions. If that's the right link.
( Newington, Wed 27 Aug 2008, 10:01, archived)

nope, finally got the link to load
you're both right, the article maitains that human emissions won't matter. I still think it's wrong though. even at a basic thermodynamic level, temp isn't the only thing that effects a liquid/vapour equilibrium.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 10:04, archived)

Most of the earth's surface is water.
It's a fairly simple diffusion model: an(effectively) infinite supply of water and a finite volume of gas in a (sort of) closed box. So temperature pretty much _is_ the only important thing.

edit: is that right? where's the back of an envelope when you need one?

edit edit: yes ... I think that's right ... god it's a good job I don't do much science for a living any more
( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 10:10, archived)

not strictly
because that assumes atmospheric temperature is the only cause of water vaporisation, which isn't really the case. The atmosphere is capable of holding more water for short periods on a localised basis .. I dunno, it's quite difficult for me to explain my reasoning behind this on the internet, so I'm not really expecting anyone to be convinced. It's something I've looked into a fair bit (one of my students is working on fuel cells)

one problem with the temp equilibrium argument around global warming though is that it opens a tiny door for the twats that say "ah but see, look at temp equilibriums and solubility, CO2 levels are actually rising BECAUSE of temp increases nernenerneneeeer .. and then I have to kill them.
( the mighty badger Aphrodite, on a bar stool, by your side, Wed 27 Aug 2008, 10:21, archived)

Sorry. That's not quite what I meant.
Water will evaporate at the surface (pretty much irrespective of temperature). The water vapour will diffuse into the rest of the volume of gas until it equalises. In an entirely closed system that would mean that eventually you'd get 100% saturation. But the actual equilibrium will be considerably below that because there are sinks of water vapor. The temperature dependence is not in how much water enters the system from evaporation, it's in the position of that equilibrium. Pumping additional water vapor into the system won't affect that equilibrium point, it will just affect how you reach it.

It'll have local effects on the weather of course ... you'll probably get much prettier clouds above cities.
( Dr. Shambolic je suis charlie, Wed 27 Aug 2008, 10:33, archived)