450 million years ago, CO2 levels were 10X current values and Earth was in an ice age.
Venus is hot because it has an atmospheric pressure almost 100X that of Earth. The same reason why the top of the Grand canyon is cold, and the bottom of the Grand Canyon is hot. Temperatures in Venus troposphere at the elevation where pressure is 1 bar, are similar to earth. Only a complete moron would believe that adding 0.0001 mole fraction CO2 to the atmosphere would cause that.
Enter Carl Sagan and Steven Hawking.
Every climate scientist in the world knows that Hawking’s claim is complete garbage, but none will speak out because they hope to benefit from his stupidity.