Monday, December 9, 2013

Analysis finds both water vapor & increased CO2 act as negative feedbacks to cool the Earth surface

A post today from physicist Clive Best's blog demonstrates why both increased CO2 and water vapor act as net negative feedbacks to cool the earth surface, the opposite of climate model assumptions.

Lapse rate feedback

In the tropics the tropopause is much higher in altitude than in temperate regions. The reason is for this is that warm ocean surfaces cool by evaporation moving latent heat upwards where it heats the upper atmosphere through condensation. The lapse rate moves towards the moist lapse rate. The tropopause is where the lapse rate peters out because radiation from GHGs to space dominates over convection. The tropopause is much higher in the tropics because there is so much water vapour in the atmosphere that radiation can only dominate where H2O wavelengths are no longer opaque. Despite this the temperature at these heights is not less than in temperate zones and the radiation loss is significant. This shows how the troposphere lapse rate and height is defined by greenhouse gas concentrations. If you add more water vapour to the atmosphere the troposphere increases in height. This is a negative feedback because more H2O does not lead to enhanced surface warming. On the contrary surface temperatures are stabilised by evaporation
What then happens if you add more CO2 ? Essentially the same negative feedback must occur. The effective height for CO2 radiative cooling to space increases to an initially colder level so leading to a slight increase in forcing. This slight forcing at the surface must also lead to more evaporation from the ocean reducing the lapse rate and thereby increasing the temperature of the effective height for CO2 radiation to space. The result is a negative feedback counteracting the original CO2 forcing.
This same effect happens every day in the tropics as solar radiation increases around midday then so too does evaporation. This is a strong negative feedback keeping ocean temperatures below ~30 deg.C . Exactly the same effect must occur for CO2.
I have been away from the UK for 5 weeks in Australia and Vietnam. Even Darwin ocean temperatures are below 30c while the air approaches 100% relative humidity and 38 C during midday. It then rains most days cooling the surface. Extreme temperatures only occur in deserts where there are no evaporation sources. Otherwise the oceans stabilise temperatures on Earth.


  1. Gas, oil, coal and biomass are the only real "green" fuels; CO2 makes plants grow, nothing green about windmills, solar or hydroelectric power. CO2, as all other normal gases in our atmosphere cool the planet, although the concentration of CO2 (~400 ppmv with man contributing 12 ppmv) is so small, man could never measure its cooling effect.

    Man did cause global warming via CFC destruction of ozone that allowed the stratosphere to cool some 1.5 C and the earth to warm some 0.6 C from 1966 to 2002. However, the Montreal Protocol, came into effect in 2000 and all CFC production facilities in developed nations were shut down. Since 2002 there has been slight cooling on earth as the stratospheric ozone has started to increase. It will take until about 2100 before stratospheric ozone gets back to normal. Thank you for recognizing the cooling effect of CO2.

  2. Konrad says:
    December 11, 2013 at 5:24 am
    “CO2 global warming question has so far been treated from a “radiation only” perspective”

    Dr. Gray is close to “getting it”, but not quite.

    The net effect of radiative gases in our atmosphere is cooling at all concentrations above 0.0ppm.

    To understand this, you only have to understand 4 simple points -

    1. Radiative cooling at altitude is critical to continued strong vertical tropospheric circulation in the Hadley, Ferrel and Polar tropospheric convection cells.
    2. The observed lapse rate below the topopause is a result of strong vertical circulation of gases across a gravity induced pressure gradient.
    3. Incident LWIR cannot heat nor slow the cooling rate of liquid water that is free to evaporatively cool. (sorry Willis, but empirical experiment proves you wrong)
    4. Without radiative cooling at altitude and the resultant strong vertical tropospheric circulation, our atmosphere would trend isothermal, with its temperature driven by surface Tmax, not surface Tav. (sorry Dr. Spencer, but empirical experiment proves you wrong)

    That’s it. That’s all you need to know. Adding radiative gases to the atmosphere will not reduce the atmospheres radiative cooling ability. Global warming is a physical impossibility.

  3. Yes, the feedback must be either very nearly neutral, or negative, as I discussed here. -Bart

  4. Ian W says:
    June 28, 2014 at 5:47 am
    Geoff Sherrington says:
    June 28, 2014 at 3:13 am

    Colleagues here in Australia are working on a correlation between rainfall at a site and its maximum daily temperature. At sites so far examined in detail, the conclusion seems to be that “water cools”.
    The correlation is not shown yet to be causation, but it is strong and large.
    It is plausible that temperatures might need adjustment for rainfall before they are to be used for certain purposes. If it is not already catered for, one example of a need for rainfall-corrected data sets would be estimation of climate sensitivity. Another would be the calibration of tree ring proxies, which might be better done after removal of a known growth agent, namely rainfall, from the temperature data used for calibration.

    Water as vapor and droplets raises the enthalpy of the air so a volume of air with increased enthalpy can carry more heat before rising in temperature. So the amount of heat in the atmosphere may remain constant as temperature varies with the amount of water. Temperature is the incorrect metric for measuring heat retention due to radiative gases.

  5. CO2 radiates at 15 microns, which corresponds with a temperature of 200K. The earth is around 290 K and the radiant top of the atmosphere is maybe 255 K. The climate kooks are saying that as the CO2 increases and the radiant top of the atmosphere gets higher and colder, it will be too cold to radiate as much. This is wrong. The closer the temperature gets to this 200 K, the more CO2 can radiate. To say it radiates less because it's colder is just wrong. The earth radiates more 15 micron IR than the sun, because the sun is too hot to radiate 15 microns. If the earth cooled to 200 K it would radiate the most of all. The claim the climate alarmists make, that cooling of the TOA will reduce radiation to space, shows they have no understanding of physics.

    1. Good points, and as I have noted many times CO2 acts as a cooling agent throughout the atmosphere. Also, CO2 is a bit player in comparison to water vapor, which has a much broader spectrum of absorption/emission and acts as the Earth's primary cooling agent.