The Tipping Point for CO₂ levels Is 450 Ppm

The tipping point for CO₂ levels is 450 ppm.This means ____.

A) that if CO₂ levels fall below 450 ppm there could be long-term potentially catastrophic effects
B) that CO₂ levels above 450 ppm will cause long-term potentially catastrophic effects
C) that CO₂ levels above 450 ppm will cause irreversible change
D) that CO₂ levels below 450 ppm will cause irreversible change
E) that CO₂ levels above 450 ppm will cause sea level to rise three meters