Please see:

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

Below are lecture notes from a college course:

The greenhouse effect of Venus
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
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.