How would the temperature of the Earth vary from its present level if the atmosphere were thicker? thinner?

Question

How would the temperature vary if it were cloudier? or composed of twice as much carbon dioxide?

Answer 1

The thicker the atmosphere, the more greenhouse gases get trapped, the hotter the planet.

Answer 2

If the air were thicker it would hold more heat, the atmosphere would be hotter.

If the air were thinner the air would hold less heat but the surface of the ground would be hotter in the daytime and colder at night.

As the sky gets cloudier the temperature tends to stay higher, even at night time.

It is generally thought that if the CO2 double the earth's temperature would run up dramatically.  (Venus has such a greenhouse gas effect but not due to CO2.)  In fact the recent increase in CO2 being blamed for global warming is up by single digit percents.  But controlled lab tests show that even a couple of percent increase caused the air to retain more heat.

Answer 3

As i understand it (probably wrongly) water and CO2 absorb the Infra-red radiation from the earth, causing them to vibrate and heat up. So presumebly if there are more clouds or CO2 the earth gets hotter. Having said that more couds would probably reflect more of the sun's UV radiation so it would have cooling effects also.

Consder other planets like Mercury and Venus, with thick atmospheres full of CO2 and nasty stuff, they're said to be like h**l.