Let's forget all the other stuff going on. We can forget that bacteria took out all the methane. We can forget plate tectonics. Yes children, animals eating plants and breathing started the first warm cycle. This carbon dioxide thing happened every 300 million years, exactly coinciding with tectonic cycles. Amazing. The current ice age is caused by animals not breathing.
ps. I shall call this Leeds Physics, the art of ignoring the elephant in the room.