>>939378581
>CO2 levels are being measured
Only recently. The whole "pre-industrial levels" thing was popularized by G.S. Callendar, and it was completely false. We don't really know what the levels were 100 years ago.
> It's not a matter of belief
It is if you just parrot the lies.

>>938610794
We're not even sure that CO2 level have increased and it looks like they may always have been about the same as today, at least for the last couple hundred years. The whole "preindustrial" thing was invented by Callendar cherrypicking values.