You are correct but C02 is another compound in the sky that reflects the suns gamma rays (weak yes, but still some rays go back to space). All compounds reflect the sun to some degree. A desert climate has very little compounds in the air which means the sun heats that part of the atmosphere more than other areas. A tropical climate has water vapor and C02, among others, that creates condensation that actually cools the atmosphere. The earths entire climate would only get hotter if the earth was traveling closer to the sun than normal. It very well could be given everything (generally) in science and space is a cycle.