On Aug 11, 8:26*pm, Roger Coppock wrote:
On Aug 11, 8:17*pm, Roger Coppock wrote:

Please see:

http://www.youtube.com/watch?v=mu1PicT0TMU

Below are lecture notes from a college course:

The greenhouse effect of Venus

--- Venus' perpendicular solar flux is ~2600 W/m2

From geometry, we can calculate the average solar flux over the
surface of Venus. It is approximately 661 W/m2.
Venus is very reflective of sunshine. In fact, it has a reflectivity
(or albedo) of 0.8, so the planet absorbs approximately 661 X 0.2 =
132 W/m2.
By assuming that the incoming radiation equals the outgoing radiation
(energy balance), we can convert this into an effective radiating
temperature by invoking the Stefan-Boltzmann law (total energy = _
T4). We find that T=220K.
But Venus’ surface has a temperature of 730K!!!
The explanation for this huge discrepancy is the planet’s greenhouse
effect.

The greenhouse effect of Earth

--- Earth's perpendicular solar flux is ~1350 W/m2

From geometry, we can calculate the average solar flux over the
surface of Earth. It is approximately 343 W/m2.
The earth has a much lower albedo than Venus (0.3), so the planet
absorbs approximately 343 X 0.7 = 240 W/m2.
By assuming that the incoming radiation equals the outgoing radiation,
we can convert this into an effective radiating temperature by
invoking the Stefan-Boltzmann law (total energy = _ T4). We find that
T=255K.
Earth’s surface has a temperature of 288K
While much smaller than Venus’ greenhouse effect, earth’s is crucial
for the planet’s habitability. Without the greenhouse effect, the
temperature today in Los Angeles would be about 0 degrees Fahrenheit.

Venus' surface atmospheric pressure is about 90 times that of
earth. Venus's surface gravity is about 10% less than that of earth
so Venus's atmosphere, just about all CO2,, is about 100 times as
dense as earth's.

CO2 makes up not quite 0.04% of earth's atmosphere, so Venus has about
100/0.0004 = 250,000 times as much CO2 as earth.

From

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

and

http://www.geo.utexas.edu/courses/38...ures/chap2.pdf

that 250,000 times as much CO2 on Venus results in a magnification of
warming from

132 Watts /m^ 2 to about 16,127 watts/M^2 or an effective 16,127/132
= 122 atmospheres.

122 venus atmospheres *1earth atmosphere/250,000 venus atmospheres =
0.000488 atmospheres warming, or about 0.18 watts.

Comparing the global warming caused by Venus' atmosphere to global
warming caused by Earth's CO2 doesn't cut the mustard. Obviously
many bands are saturated, making increases in CO2 much less effective
than a linear ratio would imply.

Incidentally the general consensus is that , a doubling of CO2 would
increase the flux by about 3.7 watts.

From Trenbeth's figures

http://www.cgd.ucar.edu/cas/Trenbert...TFK_bams09.pdf

the flux at earth's surface is about 492 watts, giving us a
temperature of about 288 K.

Plugging in that 3.7 watt increase, and remembering that temperature
is roughly proportional to the 4th root of the wattage flux,

(493.7/490)^0.25 = 1.00188

for a temperature increase of 288*0.00188 = 0.54 K

- A. McIntire