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

Carbon-di-oxide is considered as a pollutant because it is a green-house gas which is responsible for the global warming. This results in change of earth’s climate. Along with that excess CO₂ is harmful for the plants. Increased CO2 levels changes physiology, growth and chemistry of plants. High CO2 concentration also causes suffocation, hard breathing and choking issues.