There have been only other period in geological history with CO2 levels as low as today's, the Carboniferous.
The atmospheric CO2 level was twenty times today's level during the Cambrian period, with no catastrophic consequences.
BTW when they talk about ppm is it ppmv volume or particulate. A CO2 molecule is very small, so if you evaluate a cubic foot of air the amount of CO2 is very very small in a volume sense. As a particulate, then it has to be weighed against say water molecules H2O which combine from sub micron size to big drops, again it is insignificant. Water vapor has 10 times the impact on the heat levels.
I have worked with PhD who don't know the difference between ppm and ppmv, Do you think that the lawyer politicians have a clue?