A radical but rather elegant theory has been proposed by a Hungarian Physicist Ferenc Miskolczi (see refs) that the Earth maintains a maximised greenhouse effect to allow the Earth to cool as efficiently as possible. This self-regulation arises because 70% of the Earth’s surface is water allowing both cooling through evaporation (latent heat) but also warming through H20 being a greenhouse gas. Unlike CO2 the concentration of H2O in the atmosphere is governed by thermodynamic processes. Local thermodynamic equilibrium in the atmosphere ensures equality between the absorbed IR energy by all greenhouse gases from the surface and the IR energy emitted back to the surface by those same gases. Water evaporation and convection drives the Earth’s weather systems. Water Vapour also dominates the greenhouse effect of the Earth but has two subtle feedbacks. Firstly evaporation mainly from oceans is a very efficient way for the surface to loose heat through latent heat. However cloud formation then leads to a higher albedo and to night time heat retention so there is a play-off beween this and the greenhouse effect of H2O. Miskolczi and Zagoni argue that the total average greenhouse effect on Earth depends only on the input energy of the sun plus a small geothermal component. This simple conclusion is backed up by detailed radiation transmission model calculations and data comparisons.
The total greenhouse effect remains exactly what is needed to maximise cooling of the Earth. Any man-made CO2 increases are simply offset by a small decrease in water vapour so as to maintain thermodynamic equilibrium. They claim that the data show there has been a small 1% decrease in global humidity to offset all CO2 increases caused by human emissions. The following slides try to explain the energy balance arguements they make. The crucial proposal is that the water content of greenhouse concentrations (H2O + CO2 + CH4) are maintained to be such that half the IR energy radiated from the surface is emitted into space from the top of the atmosphere while another roughly 60 watts/m passes clean through the IR wavelength window. The physics motivation for this first proposal is the virial theorum which states that the kinetic energy (heat) of the atmosphere is half the (gravitational) potential energy. The effective radiative kinetic energy is associated with the IR radiation emitted from the atmosphere to space(Te**4). The effective potential energy is associated to the IR radiation emitted from the surface (Ts**4). The second proposal is that the amount of energy emitted back to the surface is equal to that absorbed by the atmosphere. This is based on an assumption of overall local thermodynamic equilibrium (Kirchoff law). With these two assumptions the normalised greenhouse factor is and will remain equal to 1/3. The Earth’s temperature remains fixed unless the input energy changes through volcanic or human induced aerosols, or through changes in the Earth’s orbit. The temperature is however independent of any anthropogenic CO2 increases.
Global Circulation models assume that rises in CO2 concentration lead to an enhanced greenhouse effect with rising temperatures causing yet more evaporation of H2O leading to an enhanced warming . This is the positive feedback which leads IPCC to give scary predictions of 3-7 degrees rise in global temperatures in the next 50 years or so. The effect of CO2 increase on the greenhouse effect alone would lead to less than a 1 degree rise.
The Saturated Greenhouse theory says that exactly the opposite happens. The Earth has an infinite amount of greenhouse gas available to it in the form of water, but the average relative humidity today at the surface is 78% and just 37% at 9000 m. So why isn’t it 100% ? The reason Miskloczi argues is that energy balance between the surface and the atmosphere (Kirchoff: ED = AA ) plus a requirement that the kinetic energy of the atmosphere = 2* the potential gravitational energy (Virial theorum: EU = 2SU) causes a saturated greenhouse effect therefore limiting the Earth’s temperature to its current level. The normalised greenhouse effect = 1/3 and will always remain so and the Earth’s temperature remains constant unless the external energy parameters change (solar). Therefore to compensate for any rises in CO2 levels the Earth will adjust the relative humidity to maintain the same thermal equilibrium.
The super El Nino effect in 1998 led to a rise in global temperatures. If it were the case that a temperature rise causes more water vapor through evaporation, causing yet more temperature rise, then one would expect temperatures to continue to rise after 1998, and result in a run-away effect. But the opposite happened, because temperatures fell as the greenhouse equilibrium mechanism restored the balance. The extra greenhouse gases rained out to restore the equilibrium. Miskolczi is arguing that exactly the same effect is happening now as has happened in the past with any sudden perturbation in CO2 levels. Energy balance of the Earth/Atmosphere will cause water vapour content to increase or decrease in order to maintain an equilibrium situation with a saturated greenhouse effect g=1/3. In order to offset a potential doubling of atmospheric CO2 levels caused by human activity the relative humidity would reduce by 3%. Miskolczi claims that existing data show that already a global reduction of 1% in relative humidity has occurred over the last 100 years. Data from NOAA Earth System Research Laboratory for the upper atmosphere show that relative humidity has indeed been falling.
This theory depends on the two assumptions of local thermodynamic equilibrium (Kirchoff) and the applicability of the Virial theorem to the radiation fluxes from the surface and the top of the atmosphere. Mainstream IPCC scientists have all attacked this but direct measurements do really seem to support these assumptions. The pressure distribution of the atmosphere is a function of gravity and temperature P(h)=Po*exp(-mgh/kT). The effective black body radiation emitted by the atmosphere to space by greenhouse gases is a kind of measure of it’s “greenhouse” temperature and hence its kinetic energy, whereas the radiation emitted from the surface is related to the Po the pressure at height zero and hence the gravitational potential energy. I certainly will need to think harder about this one to be convinced, but the theory is very attractive and if true would completely overturn mainstream climate change predictions.
Ferenc M. Miskolczi, “Greenhouse Effect in Semi-Transparent Planetary Atmospheres“, Quarterly Journal of the Hungarian Meteorological Journal, Vol. 111, No. 1, January – March 2007.