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

Carbon dioxide is necessary for plants. Why do we consider it as a pollutant?
Answer:
Plants require C02 in an optimum amount for the process of photosynthesis. But, high concentration of (more than normal) C02 is harmful and considered as a pollutant. Higher concentration of C()2 is one of the causes of greenhouse effect and global warming as it absorbs the infrared radiations thus increasing the temperature of Earth. This leads to many environmental problems.