What would the Earth's climate be like if we DOUBLED the amount of the GREENHOUSE GASSES in the atmosphere? TOO COLD for humans. Greenhouse gasses cool off the planet.
TOO HOT for humans. Too many greenhouse gasses will trap too much heat.
BETTER than it is now for humans. More greenhouse gasses are always good.
The SAME as it is now, because greenhouse gasses DON'T AFFECT the atmosphere.
We DON'T KNOW...There's NO EVIDENCE to tell us what would happen.