And Earth once was frozen all over, and there were times when concentration of greenhouse gases was much higher than it is today, with no "runaway" effects.
Do you seriously not realize that the people who've been doing climate research for decades are aware that there were previous eras with more CO2 in them?
If you weren't just out to validate your own political goals, you might stop for a moment and reflect on how poorly-suited current life on the planet is for those previous eras with drastically more carbon in the air.