Well, ignoring climate change for a moment. The Sun is still the source of the heat, but it is more or less constant. The atmosphere is just the tin foil around the potato.

Put another way: if the sun were to vanish, the earth would cool very quickly. Probably we’d all be dead within a month. I’ve never run that calculation. Would actually be fun to do the calculations. But the sun can’t just vanish, so ultimately it’s navel gazing.

I presume your comment was related to climate change and atmospheric composition though.