The case for us emitting the CO2 is quite strong because of the ratio of the Carbon-14 isotope in the atmosphere, which is consistent with the increase being due to burning of fossil fuels (and also matches with estimates of how much fossil fuel has been burned iirc).

I agree there is nothing linear about the climate, but I don't think the greenhouse effect of CO2 is in doubt. CO2 traps infrared radiation in the atmosphere and prevents it from escaping to space, and thus has a heating effect on the lower atmosphere and the Earth surface.

Concerning adaptation: I agree with you, we'll adapt to anything because we have no choice, and what exactly will happen (and when) is anyone's guess.