In the second episode of the original documentary series "Stephen Hawking's Favorite Places," the theoretical physicist used the planet Venus to explain how things could go wrong for a planet.

In the findings of a study conducted by the National Aeronautics and Space Administration (NASA) in 2002, it was suggested that Venus shared similar traits to the Earth and even had water around 4.5 billion years ago. However, as the planet increasingly warmed, more water vapor was in its atmosphere resulting to more heat being trapped which continued until its oceans completely evaporated.

"Venus is like Earth in so many ways," Hawking explained. "A sort of kissing cousin. She's almost the same size as Earth, a touch closer to the sun. She has an atmosphere."

Using rudimentary computer-generated imagery (CGI), Hawking can be seen being trasported to Venus as he passed through clouds of sulfuric acid in the episode. However, he finds that the pressure on the planet is roughly 90 times that of the Earth "enough to crush a submarine," while the temperature is around 200 degrees. He explains that the Earth could find itself in a similar situation if greenhouse gases are not controlled.

Upon returning to the Earth from his trip to Venus, Hawking proposed a salutation to those who deny science, instructing the viewers to tell a climate denier to take a trip to Venus, even offering to pay for their fare. 

Hawking had previously stated that humans are treating the Earth so badly that we are eventually going to have to leave this planet and colonize another inhabitable celestial body in approximately 100 years. The United States withdrew from the Paris Climate Agreement, which led to speculations that the leaders of the country are deniers of climate change. 

The Paris climate agreement is an international effort to reduce greenhouse gas emissions and was signed by 195 nations in 2015.