THE COOLING EFFECT OF GREENHOUSE GASSES
A comparison of the average temperature of planet Earth to that of Venus, Titan, Jupiter and Saturn reveals the 40C (or 40K) degree cooling effect of "greenhouse gasses."
Despite the noise in media and government, the true effect of greenhouse gasses in the atmosphere of a planetary body is to make it more efficient at shedding heat back to space.
Firstly, we can define what have been labeled as "greenhouse gasses" as gas molecules with three or more atoms, water vapor, carbon dioxide, and methane, H2O, CO2, and CH4. Because of their size, they are reactive to heat carrying infrared light wave spectrum.
Secondly, Ideal Gas Law - PV=nRT, shows that temperature is proportional to Pressure and Volume. Given that the atmosphere of Earth and other bodies is contained by gravity, we can strike Volume from the equation for the sake of comparison. The comparison can be made at points of equal atmospheric pressure.
Average temperature of planet Earth is calculated as the average temperature of its atmosphere at sea level, or 1 Bar. Data from NASA provides us the temperature of Venus, Titan, Jupiter, and Saturn at this same point of atmospheric pressure.
Because the heat with the atmosphere of a body within our solar system comes from the Sun, it's distance from the Sun determines how much energy it receives. To calculate the difference in energy between the Earth and other bodies we will use the Inverse Square Law. For example; Venus at 67M miles from the Sun compared to the Earth's 93M miles receives almost twice as much energy. 93/67 Squared = 1.9267. While Saturn and Titan at 880M miles from the Sun receive only 1% as much solar energy. 93/886 Squared = .011.
Next, we can use the Stefan-Boltzmann Law of thermal Radiation to determine much energy we can expect to find at points 1 Bar in the atmosphere of different bodies;
the total radiant heat power emitted from a surface is
proportional to the fourth power of its absolute temperature.
To make our comparison, we must make our calculation of absolute temperature by using the Kelvin Scale, wherein zero degrees K shows a complete absence of thermal energy. Relative to the Celsius Scale: (x − 273.15) °C. So the average temperature of Earth's atmosphere at sea level expressed as 15 degrees Celsius, is 288K.
Data from NASA and the Magellan (1991), Galileo (1995), and Cassini-Huygens (2005) probes to Venus, Jupiter, Titan and Saturn shows the average temperature at 1 Bar, and atmospheric composition as follows:
Venus: Greenhouse gasses, Yes - 96.5% CO2
Distance from the Sun - 67M miles
Average Temperature at 1 Bar - 339K
Titan: Greenhouse gasses, Yes - 5% CH4
Distance from the Sun: 880M miles
Average Temperature at 1 Bar - 94K (1.4 Bar at the surface)
Saturn: Greenhouse gasses, NO
Distance from the Sun: 880M miles
Average Temperature at 1 Bar - 134K
Jupiter: Greenhouse gasses, NO
Distance from the Sun: 490M miles
Average Temperature at 1 Bar - 165K
Comparing the atmospheric temperatures at 1 Bar between Venus and Earth, for example, is made as follows:
(Fourth Root of ((Earth Distance from the Sun/Venus Distance from the Sun) Squared)) x 288K; or (Square Root of (93/67)) x 288K.
Distance from Avg Temp. at 1 Bar Comparison Difference
the Sun as measured by NASA to Earth
Venus 67M 339K 339K 0
Titan 880M 94K 94K 0
Saturn 880M 134K 94K + 40K
Jupiter 490M 165K 125K + 40K
As we can see, Saturn and Jupiter with no greenhouse gasses measured a thermodynamic equilibrium of temperatures 40K higher than Venus and Titan when compared to Earth at points of equal atmospheric pressure. While Venus and Titan showed thermodynamic equilibrium exactly the same as Earth, with atmospheres containing 96.5% CO2, and 5% CH4 respectively. Thus, the cooling effect of "greenhouse gasses."
