# Flux question

1. Jan 20, 2004

### Brad_Ad23

Ok, here's the question.

Without the greenhouse gases in earth's atmosphere the temperature would be 250K. With them it is 40K higher (290K). Using the Stefan-Boltzman equation for flux ( F = &sigma;T4) what is the percentage of infrared radiation leaving the earth's surface taht is absorbed by the greenhouse gases?

I spent awhile on this and the best I could come up with is 18%. But if someone else knows how to do this, help will be appreciated. Thanks!

2. Jan 21, 2004

### HallsofIvy

Staff Emeritus
What is the &sigma;? Post that and show how you used it to get 18%.

3. Jan 21, 2004

### Brad_Ad23

&sigma; is the Stefan-Boltzman constant... 5.67 x 10-8 J/m2K4.

I basically calculated the flux F1 for T = 250K and F2 for T = 290.
Then I did xF1= F2-F1 and solved for x.

4. Jan 22, 2004

### HallsofIvy

Staff Emeritus
Okay, now what did you get for F1 and F2? I don't get 18%, I get 81%!

5. Jan 22, 2004

### Brad_Ad23

Hmm, yes I got 81% too. But for some reason it looks like I then did 1-x.

Is the basic setup even right for approaching this problem?

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