Handout on Introduction to Carbon Cycling
The Global Carbon Cycle
Below is a diagram of the global carbon cycle.
The carbon cycle has existed on earth for a long, long time. However, there is a new release of CO2 to the
atmosphere. “New” in the last 150 years. This is the CO2 released to the atmosphere by burning oil, gas and
coal. Oil, gas and coal are called fossil fuels because they are actually very ancient decayed, buried and
compressed plant materials from the Jurassic period. And, there is another human activity that releases CO2
into the atmosphere. Logging and land clearing in tropical forests is followed by burning of the remainder
slash and it releases CO2 into the atmosphere.
Look at the diagram below. Which exchanges of CO2 with the atmosphere are part of the global carbon cycle
as it has always existed, and which are recent and the result of human activities?
Global Carbon Budget
How much carbon is stored in the atmosphere, land and oceans?
How much carbon flows between the different components?
The amount of carbon on earth and in the atmosphere is such a big number that it can be difficult to grasp.
The diagram below is called a carbon budget, and shows the amount of carbon in the atmosphere, on land and
in the oceans. Carbon is shown by its weight, or mass, in Petagrams, Pg.
Land - Atmosphere
How many Pg of CO2 go from the land into the atmosphere each year?
How many Pg of CO2 go from the atmosphere to the land?
Please note - on average, the exchange of CO2 between land and the atmosphere is in balance.
Ocean – Atmosphere
How many Pg of CO2 go from the ocean into the atmosphere each year?
How many Pg of CO2 go from the atmosphere into the ocean?
Please notice - on average, the exchange of CO2 between the ocean and the atmosphere is in balance.
Fossil Fuels
How many Pg of CO2 go into the atmosphere from the burning of fossil fuels?
Which is greater – the amount of CO2 put into the atmosphere from fossil fuels or from the ocean?
Which is greater – the amount of CO2 put into the atmosphere from fossil fuels or from the land?
So why is CO2 from fossil fuels such a big deal!!! Its small compared to the natural carbon cycle!
Because, fossil fuel CO2 is a recent addition to the atmosphere, and instead of being in balance, the amount of
CO2 in the atmosphere is now increasing. Each year the amount of CO2 in the atmosphere is growing. The
natural systems of carbon cycling can not remove all of this new CO2 from the atmosphere. The problem is that
the earth has never before experienced an atmosphere with as much CO2 as it has currently.
Amounts of carbon – what are the units?
Petagram
A petagram (Pg) is a measure of mass, or weight.
A petagram is = 1,000,000,000,000,000 grams (that’s 15 0’s).
So, how much is that?
1000 grams = 1 kilogram.
1 kilogram = 2.2 lbs.
2240 lbs = 1 ton.
So 1 petagram (Pg) = 984,206,527 tons
That number is 984 million, 206 thousand, and 527 .. .tons!
What weighs about one ton?
A 1985 Volkswagon beetle weighs about 1 ton.
1 Pg = the weight of over 984 million Volkswagon beetles.
Now, go back and look at how much CO2 is in the atmosphere.
Gigaton
Want to try a Gigaton?
PPM
Teach about concentration and PPM