Earth Science Question..please help?

[Golden_Child]

Explain how the temperature of earth would vary from its present level if the atmosphere were:

A. Thicker
B. Thinner
C. Cloudier
D. Composed of twice as much carbon dioxide

[Angela S]

That's a great question.

By thicker or thinner it depends on whether you mean geometrically thicker or optically thicker

Certainly increasing the CO2 would trap more energy in the form of heat and thus the temperature would increase.
Thinner should indeed leads to a decrease in temperature, because the trapping of heat by the atmosphere should be less effective, and the inverse is true for a thicker atmosphere.

But cloudier is a challenge. Clouds are water vapor and water is a greenhouse gas. So there is a battle between albedo and the greenhouse effect. The clouds ought to lead to less absorption of sunlight due to increased albedo - but what is hitting the ground will be trapped more effectively.
Take a look at Venus - the albedo is high and the cloud cover is complete (we can;t see the ground) - but the greenhouse effect wins over albedo - Venus is incredibly hot at the surface (700K).