"The scientists knew that their theories of our solar system's evolution could not account for the temperature on Venus, and to allow any consideration of a cataclysmic explanation would have supported Velikovsky. They had to produce a theory to explain the high temperature, that also allowed Venus to be as old as the rest of the planets. Eventually, they produced a theory that blamed the CO2 which makes up 96% of the Venusian atmosphere. This was the "greenhouse" effect."
Even a stopped clock is right twice a day.
Velikovsky was a loon. He exemplifies the danger when an expert in one field comes to believe he is an expert in all fields.
Velikovsky was quite thoroughly dispatched by Isaac Asimov in his essay, Worlds in Confusion.
Velikovsky (I am working from memory here) claimed that Venus had an atmosphere made of hydrocarbons. This is false.
He could not account for the lack of eccentricity in Venus' orbit.
He could not explain why Venus' orbit follows the Bode-Titus law.
And, most laughable of all, Velikovsky admitted his theories were incompatible with Newton's Laws of Motion, and then recommended that Newton be revised to match his (Velikovsky's) theories!