Here is my theory: Once heat radiation enters our atmosphere from the sun and gets absorbed by the material inside, it is emmitted back as conduction/convection. In order for this heat to travel it needs a medium such as air. Now isn't it true that once this heat reaches the border between atmosphere and space it stops? Therefore this would be an explaination for global warming since most of the heat entering the atmosphere gets blocked inside, regardless of carbon dioxide. It would also explain why the further up in altitude you go the colder it becomes, because the density of air goes down the higher you go. Therefore there would be less possibility for heat to travel upwards since the space between 2 neighbouring air molecules increases. Am I correct?