Plants need CO2 to breathe just like we need Oxygen...in fact..the way it works is that plants 'inhale' CO2 and 'exhale' Oxygen...we do the reverse...

it's called an ecosytem

at 400ppm...plants are BARELY hanging in there...they are literally gasping for air..

During MOST of the earlier history of earth the CO2 level in the atmosphere has been MUCH higher...+1000 ppm many times.

Today...evil hateful people..the greens...are conspiring to cause another major extinction event. They are trying to cut back on the CO2 in the air....

which will kill all the plants..

and then kill all life on Earth.