Does the greenhouse effect trap heat Venus?

Yes - the atmosphere of Venus is 90 times more dense than that

on Earth and it is made of 96.5% of CO2 and a 3% of nitrogen.

Interestingly there is almost no water in the atmosphere of Venus.

Because water vapor is a lighter gas than CO2, water vapor and

other lighter gases would tend to rise and be swept away by the

solar wind. By comparison, the atmosphere of earth is about 70%

nitrogen, 29% oxygen and 1% other gases like argon, water vapor,

helium, nitrogen, and a smidgen of CO2 (about 0.04%).

On earth, most of the greenhouse effect is due to water vapor.

Water vapor causes between 36% and 66% of the greenhouse effect on

Earth for clear sky conditions and between 66% and 85% when

including clouds - depending on how cloudy an area is. The rest of

the greenhouse effect is attributed to methane, CO2, nitrous oxide,

and CFCs.

Because of the denser atmosphere and the chemical composition

Venus experiences an intense green-house effect that raises the

temperature over the surface to more than 470ºC. Clouds are common

on Earth but they completely cover Venus' atmosphere. They are made

of sulfuric acid droplets at 50-70 km above the surface and at

temperatures comparable to Earth's surface temperatures. Once solar

energy penetrates the clouds, they act like a blanket to keep the

heat in. You see the same phenomena on earth where cloudy winter

nights tend to be warmer than winter nights with clear skies.

The denser atmosphere of Venus also adds to the greenhouse

effect there. The added density is like throwing on more blankets

to keep you warm in bed. The more blankets you have, the less heat

can escape.