Re: [Phys-l] Greenhouse effect / 2nd law

[John Denker <jsd@av8n.com>]

On 04/25/2011 04:36 PM, Folkerts, Timothy J wrote:
> This is connected to the GH effect in that they have trouble
> believing energy can travel from the "cool" air to the "warm" earth
> and cause any warming of the surface.

OK.  I understand the second part of the question now.

Dynamic equilibrium (as previously discussed) helps with the
first part of the question.  Moving on now to the second part
of the question, the following may help:

The air is cooler than the earth, but it's a whole lot warmer
than outer space, which during the night is the alternative.

If you've ever been out in the desert at night, you know
this.  Standing under a ramada feels treeemendously warmer 
than standing out in the open.  The ramada is cooler than
you are, but it's verrrry much warmer than 3 kelvin.

In situations where/when there are clouds, or plain old humidity
in the air, you don't lose nearly so much (net) heat at night.
It turns out that H2O is the #1 greenhouse gas, by a wide margin.

This is not a small effect.  In the desert it is routine to
have diurnal temperature swings of 15 degrees C.  That's a
difference of 27 degrees F from morning to afternoon.  Swings
of 20 degrees C (36 degrees F) are not uncommon.  Here is
some current data:
  http://forecast.weather.gov/MapClick.php?CityName=Gila+Bend&state=AZ&site=PSR&textField1=32.9478&textField2=-112.716&e=0

			Tonight Lo 60 °F	
Tuesday Hi 91 °F	Tuesday Night Lo 58 °F	
Wednesday Hi 93 °F	Wednesday Night Lo 62 °F	
Thursday Hi 98 °F	Thursday Night Lo  65 °F	
Friday Hi 96 °F 	Friday Night Lo 64 °F

If/when there is some humidity in the air, nighttime temperatures
do not drop nearly so much.

If anybody doesn't believe the "cool" air is warmer than
outer space, let him walk around in the desert at night for
a few minutes.