Greenhouse Effect

[Rassilon]

How would one compute the greenhouse effect of other planets? Say I were doing this in Celestia and I had Earth with an Atmospheric height of 60...I suppose I would have to add a variable that holds the amount of CO2 in the atmosphere for a start I suppose unless there is a simpler method for calculating this...I already have in mind how I am going to do surface temprature based on long and lat coordinates roughly...I just need a basis to start with is all...

[Evil Dr Ganymede]

I would love to know this myself.

I remember seeing a formula on a worldbuilding website that had terms for atmospheric density and partial pressure of greenhouse gases (IIRC, the atmospheric density was actually more important) but I can't find it now..

EDIT: This isn't what I was thinking of, but it might be useful...
http://www.fact-index.com/g/gr/greenhouse_effect.html
http://www.globalchange.umich.edu/globa ... y_balance/

[Rassilon]

Well with that information I could come up with a rough estimate....but Im sure theres a way to compute this based on the thickness of the atmosphere alone....I could then add in a percentage of greenhouse gases as a single variable to alter the sum even more...

[Evil Dr Ganymede]

Aha. Found the formula in my archives... no idea if it's accurate or realistic though (there's no references for it), but it's the best I've found. This was originally by Tyge Sj?strand, but I can't find his website anymore.

The Greenhouse gas pressure is the combined pressure, in atm, of the greenhouse gasses carbon dioxide, methane, sulfur dioxide and nitrous oxides. Water vapor is also included if it is a major part of the atmosphere. Note this combined pressure, Pgr.

GF = 1 + ((P^0.5) * 0.01 * 1d10) + ((Pgr^0.5) * 0.1) + (Wv * 0.1)

... where: P is the atmospheric pressure
Pgr is the greenhouse gas pressure
Wv is the water vapour factor

This factor is multiplied with the blackbody temperature * albedo to get the final temperature. (Wv is a factor indicating how much water vapour is in the atmosphere. It's usually between 1 and 10). The 1d10 is a random factor thrown in (it means "roll a ten-sided dice).

See where that gets you...

[symaski62]

http://en.wikipedia.org/wiki/Greenhouse_effect

[Evil Dr Ganymede]

http://en.wikipedia.org/wiki/Greenhouse_effect

That seems to be the same as the first link I found. It seems that these online encyclopaedias share their entries

[Rassilon]

I might just rely on atmosphere thickness more or less to keep it simple...Im finding this to be a bit tedious....Thanks for the great start!

EDIT: I have found a very accurate approximation using atmospheric pressure and a multiplier based on planet class. I use the same class for both Venus and Titan and to my suprise they both have accurate surface tempratures based on info I grabbed from the net...

Venus has 90 atmospheres and Titan has 1.6 atmospheres. Venus came out to be ~800 F and Titan -280 F...Not a bad start...

My formula is

ST = BBT + (AP * PCM)

ST = Surface Temp
BBT = Black Body Temp
AP = Atmosphere Pressure
PCM = Planet Class Multiplier (Or you could say amount of gasses)

The PCM for Terrain class is 30 where the PCM for Venusian os 5...

[Cormoran]

Mr Sjostrand's site has been re-organised. His World generation rules can be found here:

http://www.trisen.com/sol/static/wg/wg.html

Full of good stuff for us World-Builders

Cheers,

Cormoran

[Evil Dr Ganymede]

Ah, thanks Cormoran, I had wondered where that had got to.

Rassilon, where'd you get the approximation you used? Is there a link?

[Rassilon]

I made it up...