The Carbon Dioxide Information Analysis Center DOE

What is a GigaTonne of Carbon?
Its is one billion metric tons. That is one billion, thousand kilograms of carbon. It is a billion million grams of carbon. A trillion kilograms. One quadrillion (10¹⁵) grams, a petagram. That's just a bunch of numbers, How big is it really?

A cubic kilometer of water masses one giga tonne. The density of carbon is 2.267 gm cm^-2. So it would take 775/2.265 or 341 cubic kilometers of carbon, a small mountain range, to equal the amount of carbon in the atmosphere.

A standard coal carrying railroad car carries 100 (English measure)  tons of coal. Two thousand pounds is close enough to 1000 kilograms for this comparison. So one car is 100 tonnes as well.

10*9/10*2=10*7 so we would need a train with 10,000,000 cars to carry a giga tonne of coal. A car is roughly 50 feet long so this train would stretch 500,000,000 feet or nearly 100,000 miles. That's halfway to the moon. It would circle the earth like a belt and go around four times.

It would take 775 of these trains to carry all the carbon in the atmosphere.

A supertanker ship, an ultra large crude carrier, can carry up to 500,000 deadweight tonnes of oil. 775*10⁹ / 500*10³  suggests it would take a a fleet of 1,500,000 supertankers to carry the carbon in the earth's atmosphere. At four hundred meters in length each, we are talking about a line of supertankers that is 750,000 kilometers long. Call it 500,000 miles, the distance to the moon and back.

The average pencil contains about a gram of carbon (the "lead" is really carbon). 775*10¹⁵ pencils laid end to end would reach 775*10¹¹ miles. The sun is 93*10⁶ miles from earth, that's too close for a good comparison. Pluto is 3*10⁹ miles away. Our pencils would reach to Pluto and back a hundred times. A light year is about 6*10¹² miles. Our line of pencils would reach 1/10 th of a light year into space.

That's a lot of carbon.


Carbon Reservoirs
The diagram shows the atmosphere contains 775 GigaTonnes of carbon. Every year 210 GT of carbon are exchanged between the atmosphere and the earth (120 with the land and 90 with the sea).

Man made sources account for 7.1 GT of which 3.3 GT are added to the atmosphere. This amounts to a 1.5% increase in the earth to atmosphere exchange without a corresponding increase in the other direction.

Over the past fifty years the amount of carbon in the atmosphere has increased from 552 GT to 750GT or about 4 GT per year. It looks like most of this could be attributed to the additional manmade sources, but that fails to explain the whole story.

Carbon Based Lifeforms
Carbon is the essence of life on earth. Humans and all the other lifeforms on this planet are made of water and carbon based organic molecules. By weight humans are 18% carbon. Since the average person weights about 175 pounds (<100 Kg) and there are about 7 billion people, we the people contain 100 billion Kg of carbon. That's 0.05 giga tonnes.








one nice summary of the science