What is Global Warming?

In simple words, Global Warming is nothing but increase of average surface temperature of our Earth due to increase of level of Greenhouse gasses. Carbon dioxide is one of such Greenhouse gasses which is being increased from its usual level due to deforestation and burning of fossil fuel. Basically these Greenhouse gasses are the main cause of trapping heats within Earth's atmosphere,  otherwise heat should have been realized to outside of Earth's atmosphere.