> and we know CO2 levels on earth have reached 8000ppm in the past The last time that CO2 levels were around 8000ppm was also the time when the solar flux was

> and we know CO2 levels on earth have reached 8000ppm in the past The last time that CO2 levels were around 8000ppm was also the time when the solar flux was several percent lower. So this argument doesn't really work the way you thought it worked.