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I'm not having trouble understanding the physics. CO2 levels are now around 400ppm. During the Cambrian age it was ten times of that at around 4000ppm. If CO2 levels were so much higher before humans existed, then how did it go down? (My understanding is that plants store it by growing.) And how can we be sure that it is emissions that makes it go up, rather than killing forests that used to store it? Wouldn't it be effective to just plant a bunch of forests in our deserts that store the CO2? California used to be mostly desert, too, but then some guy from Germany came and redirected some water to make it not as much of a desert anymore and that was over 200 years ago.