It used to be 260 ppm. Yep. And at one point the surface of the planet was several thousand degrees. I assume you prefer that that not happen again even though "it's natural" and "the planet gets hotter and colder." Some do, some don't. Yep. And up until about 150 years ago there was a pretty good balance going there, Yep. And if we reduce our CO2 emissions by about 70% (which is doable) then those "formidable mechanisms" will have a chance to keep up.