More Venus Discussion
Posted by Jeff Id on June 1, 2011
On the previous thread, I made the point that the reason for Venus surface temeprature being so high was the pressure and that any gas would create a huge warming effect. Chris Colose had made the contention that CO2 is a strong gas and it is responsible for Venus having a surface temperature that could melt lead. This statement, while correct, was placed inappropriately in the middle of a discussion of Earth’s greenhouse effect so I took the moment to explain that it isn’t a realistic comparison and basically amounts to fear mongering. As always, some had contention with my point, so I will attempt to explain further below.
The surface pressure is 93 times that of Earth on Venus. Venus’s gravity is 8.87 m/s^2 whereas earths is 9.78 or about 10% greater. Venus has a surface pressure of 93 Earth atmospheres so we can calculate 93*9.78/8.87 = 102 times the mass of Earth’s gaseous atmosphere. If we divide Venus’s gas atmosphere into 102 separate layers assuming each has the same conditions as the others, each layer has an equivalent (similar) capacity for global warming to Earth’s own due to the retardation of upwelling infrared radiation. An interesting number might be an estimate of how much warming does each Earth mass layer of Venusian gas create? This is an estimate and must be taken with care as there are many effects of the high density gas and clouds in Venusian atmosphere but it is an interesting start point.
My contention was (and is) that the density of Venus’s atmosphere creates a greenhouse effect ‘capacity’ equal to approximately 102 times anything achievable at Earth’s surface. In other words, each Earth mass layer has the ability to retard the heat flow by a similar amount. Using SoD’s (venus with no atmosphere) -43 C blackbody calculation from the thread above and the actual surface temperature on Venus of 460C we see that Venus has an approximate 500C greenhouse effect from its gasses which are mostly CO2 (96.5%).
If we divide 500C GHE/~100 Earth mass atmospheres we get a total greenhouse effect from an Earth thick layer of 96% C02 of only 5C, whereas Earth with its comparatively moist atmosphere runs at about 33C of GHE by some calcs which shows that some Earthly strange and rare gas like dihydrogen monoxide is probably a lot stronger greenhouse gas than CO2. What is also interesting is that from the table Carrick linked in #82 on the previous thread, the CO2 creates an estimated 422C of those Venusian degrees of warming so the total CO2 contribution of an Earth atmosphere that was a massive 96 percent CO2 would be about 422/102 or 4.2C – according to this simplified Venus model. 96% CO2 and a zero feedback temperature rise of 4.2C! hmm.
In other words, the melting of lead on Venus is not simply related to the huge concentrations of evil CO2 but is PRIMARILY due to the huge density of the atmosphere. Also, we can conclude that Venus should be glad that 96% of the gas in the atmosphere doesn’t have the absorption spectrum of water.