On Carbon Dioxide as Earth's thermostat.

The climate alarmists are trying to denigrate water and promote carbon dioxide as the main determinant of Earth's weather and temperature. The following is my response.

One cannot really say that CO2 is the thermostat, given that the role of the thermostat is to keep the temperature within a small temperature range. Water plays the role of thermostat: in the kitchen, as long as there is water in the pot, the temperature of the boiling pot remains close to 100o Celcius (if there was some salt in the water, as water boils off, the temperature raises slightly). Water phase changes (solid to liquid to vapor) is essential to the thermostat mechanism. As CO2 level rises, temperature rises. Now the question: by how much? Given historical data, CO2 increases the temperature very slightly.

I see a number of comments on Venus and Mars. First, the planetary greenhouse effect is primarily an atmospheric pressure effect. Mars has a near zero atmospheric pressure, thus little greenhouse effect. The greenhouse effect has nothing to do with the distance of the Sun: the greenhouse effect of Jupiter, Saturn, Uranus - for the upper atmosphere - is about the same as on Earth, and with little co2 and plenty of methane.

Blackbody emission spectrum is independent of the composition (or phase, be it solid, liquid, gas) of the body. Thus a large body of O2 and N2 gas molecules can emit/absorb at all frequencies. But Earth is not at true equilibrium and thus one talks about graybody emission which depends slightly on composition. O2, N2 may have very weak absorption/emission lines in the IR but they can absorb/emit IR via collisions. The point is: if an atom/molecule is a weak absorber, it is also a weak emitter: so if they gain energy, they retain the energy longer. CO2 and H2O are strong IR absorbers so if they gain energy, they release the energy fairly quickly. The denser the atmosphere, the greater the probability that CO2 and H2O transfer the energy (by collision) to O2 and N2, instead of re-emitting. An overall increase in atmospheric CO2 brings about a heating of the lower (more dense) atmosphere and a cooling (less dense) of the upper atmosphere. A greater temperature differential develops and brings about atmospheric current dynamics which dissipates the temperature differential change.

If there were no CO2, would Earth remain solid ice? No. The weather in the troposphere will be about what we have now. All of life resides within the troposphere whose behavior is dominated by water. The role of CO2 is to accelerate the pace from going from an (supposed) initial solid-ice-planet to the current state of affairs. An absence of CO2 would delay reaching the current state by no more than a million years. From direct impact of sunlight, water will vaporize and sublimate, transferring a good part of its energy to O2 and N2 which hold on to the energy for a long time. Energy is accumulated - slowly - by the O2 and N2 molecules. Water may precipitate out as liquid or solid but not before it has transferred most of its energy to O2 and N2 molecules. Heck, if we had Argon (monatomic gas) instead O2/N2 (diatomic molecules which - unlike monatomic gas - emits readily in the microwave region), the weather - as the pattern of air currents and solid-liquid-gas behavior of water - would be quite similar to what one has now. Keep in mind that atmospheric currents bring water up to about 10-20 km above the top of the troposphere. In the stratosphere, water exists in a very fine, very diffuse body of microcrystals.

The science is not yet settled.