[Pretzel Logic]

I'm NOT saying CO2 levels never changed in the last 800k years. I'm saying that there were reasons for whatever changes occurred and they happened on a time scale shorter than a few hundred years. I don't know how large the variations were, but there's a big one happening now. Please give me a reason why it's not caused humans.

Well, one possible reason is that we're still warming from the prior ice age, and there's a clear link in the data that shows that CO2 rises AFTER temperature rises. So rising CO2 would be consummate with the current natural warming trend -- but the data suggests that warming causes increased CO2, not the other way around.

I think the main thing is, even if (for the sake of a mental exercise) we were to say that all current increased CO2 is caused by man, there is still no proven link that says "Increased atmospheric CO2 CAUSES increased temperature." As the old saying goes: correlation does not imply causation.

So there are two big holes in the "man-made climate change" argument: one is that CO2 increase seems to FOLLOW natural warming periods, two is that there is no proven link to increased CO2 CAUSING increased temperature.