Why carbon dioxide is considered as a green house gas? How does CO2 related to global warming?

CO2 is a greenhouse gas because of the way it interacts with electromagnetic radiation (light). It readily absorbs light at the wavelengths emitted by Earth, but is transparent to light at the wavelengths emitted by the sun. This allows sunlight to move through the atmosphere easily, but restricts the movement of light from the Earth to space, creating an imbalance between the amount of incoming and outgoing light energy, causing the planet to warm. Any gas with these properties is known as a greenhouse gas. It relates to global warming in that an increase in atmospheric CO2, and the resultant enhanced greenhouse effect, is believed to have caused the majority of the period of global warming that started about 150 years ago.  more