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What percentage of the air is carbon-dioxide?
Answer:
In 2011 Carbon dioxide is present in the Earth's atmosphere at about 385 parts per million by volume or 582 parts per million by mass. It is usually stated in ppm to reduce decimal and "0" confusion. This would be the same as 0.000 385 (by volume) and 0.000 582 (by mass ) as decimal fractions and 0.0385% (by volume) and 0.0582% (by mass)
According to the Wikipedia's math this is 3.0×10
15 kg (3 000 gigatonnes) of the Earth's 5.14×10
18 kg (5 140 gigatonnes) total atmosphere.
There is currently (March 2011) about 392 ppm (parts per million) in the atmosphere. This doesn't sound like a lot, but it has a powerful greenhouse effect. Considering it would be under 300 ppm without human emissions, this is a considerable upset in the balance of this greenhouse gas.