Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?

Carbon dioxide gas is essential for photosynthesis by plants- It is also a green-house gas (GHG). Upto 350 ppm (ppm = parts per million) concentration in the-atmosphere, CO₂ is both a good raw material as well as essential for keeping the Earth warm. However, when concentration of Co₂ rises (as presently it is 387 ppm), it becomes a pollutant because it-results in global warming. The global warming is quite dangerous because it tends to melt polar ice and glaciers existing on mountains, raise in the water level of oceans and submerge severals coastal areas and islands.