what is the capacity of carbon dioxide?

Carbon dioxide capacity means how much carbon dioxide can be released by a country or the world under the limit which will do harm to the balance of environment and cause drastic consequence.The atmosphere is consist of 78% nitrogen,21% oxygen and a little bit of carbon dioxide as well as fewer rare gas.According to recent survey,carbon dioxide is the main content of greenhouse gas.and too much carbon dioxide discharged into atmosphere will cause the temperature raise.in order to restrain the uptrend of temperature,a conception was come up with in Copenhagen climate change conference that we must control the amount of carbon dioxide discharge under 800 billion ton so that the temperature's increase won't exceed 2 degree Celsius.