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 = σ 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.