Carbon Dioxide is not an environmental polluting agent because it is not detrimental or poisonous to life. Carbon dioxide cannot kill living cells by altering their structure or physiology in the same way, for example, as a snake venom will. It can only suffocate an organism when Oxygen is not present at a sufficient concentration to sustain life.
http://www.biocab.org/carbon_dioxide_CO2.html
watch thisone too
http://theolympiareport.com/wwu-scientist-debunks-lawmakers-myths-about-co2-climate-change/