Venus has a very dense atmosphere with thick clouds made of carbon dioxide, water, and sulfur compounds. The dense clouds trap the heat from the sun by blocking its infrared energy from radiating back into space. The greenhouse effect is the process of trapping heat. It’s similar to the process used on Earth to keep plants warmer in the winter.

On Venus, the greenhouse effect is extreme. The average surface temperature on Venus is 865 degrees Fahrenheit, which is hot enough to melt lead. A small amount of infrared heat radiates back out into space, sort of like a leaky window venting out infrared heat at a certain wavelength.

Venus could get even hotter if the planet became volcanically active, and more greenhouse gasses entered the atmosphere. The biggest effect would occur from adding water, which would make the planet heat up quickly.

The hottest Venus can get is 1,200 Fahrenheit, but never hot enough to make the surface melt. If the lower atmosphere heated more, its infrared emission would change to coincide with the leaky window wavelength. The heat would radiate out and keep the temperature on Venus at an equal balance. At higher temperatures, the clouds would evaporate. At some point in the past, Venus probably didn’t have any clouds. As the air mass cooled, the clouds returned because the surface rocks reacted to the sulfuric acid. The water molecules were gradually destroyed by the sunlight in the upper atmosphere.