One of the favorite arguments of the climate alarmists is that CO2 will cause CAGW, similar to what is currently happening on Venus. This argument demonstrates an ignorance of biblical proportions regarding the GHG effect. Venus’ atmosphere is 97% CO2, but has a pressure of 93 bar or the pressure equivalent of 3,000 ft below the surface of the ocean. The density of the air at the surface is 67 kg/m^2, which is 6.5% that of liquid water. Technically, at the surface, the CO2 atmosphere isn’t a gas, it is a “supercritical fluid.” Basically, Venus is more a tea kettle than a hot air balloon. Liquids are far far far more effective at holding heat than gasses are. Heat moves in three ways; conduction, convection, and radiation, and only radiation is applicable to the greenhouse gas effect. Bring a pan of water to a boil and hold your hand over it. The warmth you feel will be convection and radiation. Put your hand in the water and what you feel is conduction. Clearly, a liquid can hold a lot of heat, and it has nothing to do with radiation or the Greenhouse Gas Effect.
The reason Venus is so hot is because the surface is so hot. Why is the surface of Venus so hot? Because far more incoming radiation reaches the surface than on earth. The earth has an oxygen layer that absorbs much of the incoming UV radiation to create ozone, and a magnetosphere that diverts other incoming radiation. Venus does not, so Venus simply allows far more warming radiation to reach its surface than the earth. Earth’s atmosphere acts like SBF100 lotion, whereas Venus’ atmosphere is like magnifying baby lotion.
The real problem the alarmists have with their argument is the mechanism of the GHG effect. CO2 has a very very very specific and narrow absorption spectrum. CO2’s only defined mechanism to cause climate change in through thermalizing 13 to 18µ LWIR, so global warming is the proper term. That previous sentence is worth repeating 1,000 times, and every observation blamed on CO2 should have to address how thermalizing 13 to 18µ LWIR causes the observation. The problem is when you thermalize 13 to 18µ LWIR, the associated blackbody temperature is -80°C. The GHG effect can’t explain temperatures of 467°C on Venus. The CO2 GHG effect can explain why Venus’ atmosphere remains above -80°C, but it can’t explain temperature way outside that range.
BTW, Mars has an atmosphere with a CO2 concentration similar to Venus’, but its temperature is nowhere near 467°C. Mars has an average temperature of about -63°C, but only 1% of the atmospheric pressure, but even with a thin atmosphere Mars still has more CO2 molecules M^3 than earth. In other words, Mars is a far better case study of the CO2 GHG effect, and what it shows is that CO2 helps the atmosphere stay above -80°C, and that is about it.
The surface of Venus also receives all but no solar irradiance. One of the Russian missions measured it at just 4 W/m2. Compare that to planet Earth where under clear noon day skies at the equator the surface receives circa 1100 W/m2.
This fact alone demonstrates that if there is a radiant GHE on Venus, it has to operate very differently to that claimed to operate on Earth.
Central to the radiant GHE theory is that Earth’s atmosphere is largely transparent to the short wavelength of incoming solar irradiance, but is significantly opaque to the outgoing long wave radiation which has been reradiated by the surface following absorption of solar insolation by the surface.
On Venus, the atmosphere is not transparent to the wavelength of incoming solar irradiance, it is almost entirely opaque to incoming solar irradiance and that is why only 4 W/m2 of solar irradiance reaches the surface. There is therefore little incoming solar irradiance to be absorbed by the surface of Venus and thence reradiated by the surface at a longer wavelength.
Not only is Venus a problem for the theory, but so too is Mars, since the Martian atmosphere contains, on a numerical basis, more molecules of GHGs than does the Earth’s atmosphere and yet there is no measurable GHE on Mars.
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