Which planet do scientists think had a “runaway” greenhouse effect, leading to extreme present atmospheric temperatures?

The planet that scientists believe experienced a "runaway" greenhouse effect, leading to extreme present atmospheric temperatures, is Venus.

Here are the steps that explain why:

1. Venus is the second planet from the sun and is similar in size and structure to Earth.

2. However, Venus has a very thick atmosphere, which is mainly composed of carbon dioxide with clouds of sulfuric acid, unlike Earth's nitrogen and oxygen-rich atmosphere.

3. This thick atmosphere traps the sun's heat, causing what is known as a greenhouse effect.

4. Scientists believe that Venus once had a moderate climate and possibly even liquid water on its surface.

5. However, if the water evaporated due to increasing temperatures, it would have released more carbon dioxide into the atmosphere, further strengthening the greenhouse effect.

6. This process could have continued, with the increasing heat causing more water to evaporate and releasing more carbon dioxide, leading to a "runaway" greenhouse effect.

7. This runaway greenhouse effect has resulted in Venus having the hottest surface of any planet in our solar system, with an average temperature of 467 degrees Celsius (872 degrees Fahrenheit).

8. Therefore, scientists believe that Venus is an example of a planet that has experienced a "runaway" greenhouse effect.