Comments on: New Paper Suggests Long-Term Water Vapour Feedback is Negative

By: Alan D. McIntire

Alan D. McIntire — Sun, 29 Mar 2009 19:47:40 +0000

***************
Let’s figure out what that feedback factor is:

Annual rainfall (I believe this is from Trenberth’s energy balance
paper) = 1m/year

Latent heat flux = 1000kg/m2*2.26MJ/kg/3600/24/365= 71.6 W/m2

The forcing for water vapor is supposed to be about 15 watts for a
doubling.

The increase in temperature from from a doubling of CO2, without
feedback, is acknowledged by everyone to be about 3.8 watts/m^2, which
would result in an increase of around 1C. I’ve seen actual estimates
ranging from 0.7 C to 1.2 C. With a 1C increase, the saturation level
of water vapor would increase 8%. That 8% increase implies a
[(ln 1.08)/(ln 2)] * 15 watts = 0.0770/0.6931 = 1.67 watts/m^2.
If there was NO increase in precipitation, NO change in convection, No
change in clouds, this would result in a temperature of about [(3.8 +
1.67)/(3.8)]* 1C
= 1.44 C. Right away we see that the “feedback” factors giving a 3 to 6 C increase are crap.

Trenbeth’s figures give about 390 watts in heating the surface
directly, 22 watts convection, and 78 watts in latent heat, somewhat
higher than my computed estimate of 71.6 watts/m^2. Climate models
predict an increase in precipitation less than the increase in
humidity, around 3% rather than the full 8%.
Multiplying my 71.6 watts by that 1.03 increse in precipitation gives
73.75, for an increase in watts of 2.1 in latent heat of
vaporization. The net increase in SURFACE flux with a doubling of CO2
and water vapor feedback would be
390 + 1.67 -2.1, or a DECREASE of 0.43 watts! Note that there would be
more heat in the lower atmosphere, an extra 3.8 + 1.67 watts, but much
of it would be eaten up in LATENT heat- radiated higher in the atmosphere, with actual surface temperature decreases .
Probably the increase in precipitation cannot be 3%, but
intuitively there would be SOME increase in precipitation, and in
conduction from the surface, eating up part of that 1.67 extra watt
feedback from water vapor.

Note that John Christy reported on an acutal experiment in increasing water vapor, due to irrigation of the San Joaquin Valley.

http://ams.confex.com/ams/pdfpapers/68739.pdf

Daytime temperatures dropped slightly during the summer, nighttime temperatures increased significantly due to vapor condensation at night, preventing large drops in nighttime temepratures- A. McIntire

By: Lawrence Cummings

Lawrence Cummings — Sat, 28 Mar 2009 04:34:29 +0000

There is a simplified model of heat transfer from the bottom to the upper regions of the troposphere in which convection accounts for about two thirds, condensation of water vapour (releasing latent heat of vaporisation) accounts for about a quarter and radiation accounts for less than one tenth of the heat transfer.
Using this model we see that any increase in evaporation due to higher surface temperatures will result in a less than proportional reduction in the one tenth of heat transfer due to radiation, but a proportional increase in the one quarter of heat transfer due to condensation. So, if increases in carbon dioxide force an increase in surface temperature, with a consequent increase in evaporation and water vapour, the net effect of this increased water vapour will be to cool the surface; negative feedback.
This could be a straightforward physical explanation for the negative feedback that the authors refer to.

By: admin

admin — Fri, 06 Mar 2009 14:10:52 +0000

The paper comes with a number of caveats. Roy Spencer has evidence for strong negative feedback that isn’t represented by climate models:

http://www.drroyspencer.com/2009/02/what-about-the-clouds-andy/

By: pjm

pjm — Fri, 06 Mar 2009 13:09:59 +0000

It is, I think, not in dispute that water vapour is a greenhouse gas, so water vapour produces warming. Likewise I don’t believe that it is in dispute that clouds tend to be cooling, (even though they can reduce cooling at night). This is not feedback, and I didn’t think the article was primarily about feedback, but about lowering of humidity. The conventional idea is that heating increases water vapour, increasing heating, and so on again – a positive feedback. It may of course be that heating decreases water vapour, decreasing ( and stabilising) heating – a negative feedback. But then maybe heating decreases water vapour, decreasing clouds, increasing heating – another positive feedback. Maybe some people have the data to say which of these possibilities is correct. I don’t.

For me there are three take-away messages. In increasing order of importance
– the balloon data are not consistent with the models,
– they are also not very consistent with the satellite data.
– This needs more study.

Peter

By: Tres nuevos trabajos, y muy distintos, en contra del CO2 como factor principal de cambio climático. « PlazaMoyua.org

Fri, 06 Mar 2009 09:01:30 +0000

[...] Y en el tercero, de Garth Paltridge, Albert Arking y Michael Pook, publicado en Theoretical and Applied Climatology , sugieren que la realimentación a largo plazo del vapor de agua es negativa, lo que daría al traste con la hipótesis del CO2 como factor de peligroso cambio climático, porque el vapor de agua reduciría, en vez de amplificar, la respuesta del sistema climático a una influencia externa como el CO2. [-->] [...]

By: George E. Smith

George E. Smith — Fri, 06 Mar 2009 01:23:10 +0000

Well it’s for sure that water liquid, and water solid feedback; AKA clouds is negative; given that nobody ever observed it to get warmer when a cloud passes in front of the sun; and given that those liquid and solid water amounts in the atmosphere reflect a lot of incoming solar radiation back into space (albedo increase), and then they block further amounts of solar radiation from reaching the ground; which may be the proximate cause of it getting colder when said cloud passes in front of the sun.

Yes I know the weather people say it gets warmer at night if there are clouds in the sky; but that isn’t true, it still gets colder at night because the sun is often not shining at night; even in Australia, and besides last night’s weather is not climate. More clouds means more clouds on a climate time scale; which means day and night for years.

So if water in vapor form is also negative feedback; when does it get time to play positive feedback to CO2.

Water vapor of course absorbs a good deal of incoming solar spectrum radiation, beginning at about 750 nm in the extreme red visible, and continuing on and off out to 20 microns when ti becomes totally opaque. There’s maybe 45% of the air mass zero solar spectrum energy in that range, and water vapor may get about 1/2 of it, so something in the 20-22% range, which is a pretty significant cooling effect I would think.
Yes in the IR you get some thermal radiation absorption by water vapor; but then there’s those clouds again.

Seemss to me that water in the atmosphere simply adjusts the amount of clouds at any temperature, to control the overall temperature by playing off the negative and positive feedbacks.

And water itselfr is perfectly capable of triggering a water feedback positive effect, without any assistance or trigger from CO2, and since they basically compete for the same IR spectrum; it is only the total gHG that matters, not any one species; well except for water which dominates the whole picture.

Well too bad the models don’t model the water; probably because humans don’t put out any, except from our cars, and our exhalation, and from burning fossil fuels, and other hydrocarbons.

Just wait till we have that Hydrogen economy of the future.

By: Negative feedback in climate - empirical or emotional? « Watts Up With That?

Thu, 05 Mar 2009 16:34:56 +0000

[...] I agree. Here is more on the paper and it’s conclusions. – Anthony From Climate Research News [...]