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New Paper Suggests Long-Term Water Vapour Feedback is Negative
A new paper has been published in the journal of Theoretical and Applied Climatology entitled: ‘Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data’ by Garth Paltridge1 , Albert Arking2 and Michael Pook3
(1) Environmental Biology Group, RSBS, Australian National University, GPO Box 475, Canberra, ACT, 2601, Australia
(2) Johns Hopkins University, Baltimore, MD, USA
(3) Centre for Australian Weather and Climate Research, Hobart, TAS, Australia
The Abstract states:
The National Centers for Environmental Prediction (NCEP) reanalysis data on tropospheric humidity are examined for the period 1973 to 2007. It is accepted that radiosonde-derived humidity data must be treated with great caution, particularly at altitudes above the 500 hPa pressure level. With that caveat, the face-value 35-year trend in zonal-average annual-average specific humidity q is significantly negative at all altitudes above 850 hPa (roughly the top of the convective boundary layer) in the tropics and southern midlatitudes and at altitudes above 600 hPa in the northern midlatitudes. It is significantly positive below 850 hPa in all three zones, as might be expected in a mixed layer with rising temperatures over a moist surface. The results are qualitatively consistent with trends in NCEP atmospheric temperatures (which must also be treated with great caution) that show an increase in the stability of the convective boundary layer as the global temperature has risen over the period. The upper-level negative trends in q are inconsistent with climate-model calculations and are largely (but not completely) inconsistent with satellite data. Water vapor feedback in climate models is positive mainly because of their roughly constant relative humidity (i.e., increasing q) in the mid-to-upper troposphere as the planet warms. Negative trends in q as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2. In this context, it is important to establish what (if any) aspects of the observed trends survive detailed examination of the impact of past changes of radiosonde instrumentation and protocol within the various international networks.
The paper concludes:
It is of course possible that the observed humidity trends from the NCEP data are simply the result of problems with the instrumentation and operation of the global radiosonde network from which the data are derived. The potential for such problems needs to be examined in detail in an effort rather similar to the effort now devoted to abstracting real surface temperature trends from the face-value data from individual stations of the international meteorological networks. As recommended by Elliot and Gaffen (1991) in their original study of the US radiosonde network, there needs to be a detailed examination of how radiosonde instrumentation, operating procedures, and recording practices of all nations have changed over the years and of how these changes may have impacted on the humidity data.
In the meantime, it is important that the trends of water vapor shown by the NCEP data for the middle and upper troposphere should not be “written off” simply on the basis that they are not supported by climate models—or indeed on the basis that they are not supported by the few relevant satellite measurements. There are still many problems associated with satellite retrieval of the humidity information pertaining to a particular level of the atmosphere—particularly in the upper troposphere. Basically, this is because an individual radiometric measurement is a complicated function not only of temperature and humidity (and perhaps of cloud cover because “cloud clearing” algorithms are not perfect), but is also a function of the vertical distribution of those variables over considerable depths of atmosphere. It is difficult to assign a trend in such measurements to an individual cause.
Since balloon data is the only alternative source of information on the past behavior of the middle and upper tropospheric humidity and since that behavior is the dominant control on water vapor feedback, it is important that as much information as possible be retrieved from within the “noise” of the potential errors.
See also Climate Audit: ‘A Peek behind the Curtain’
March 6th, 2009 at 2:34 am
[...] I agree. Here is more on the paper and it’s conclusions. – Anthony From Climate Research News [...]
March 6th, 2009 at 11:23 am
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.
March 6th, 2009 at 7:01 pm
[...] 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. [-->] [...]
March 6th, 2009 at 11:09 pm
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
March 7th, 2009 at 12:10 am
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/
March 28th, 2009 at 2:34 pm
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.
March 30th, 2009 at 5:47 am
***************
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