Carbon Sinks - Visualization of Quantities
 - Climate Change and Global Warming

Carbon is in a constant state of flux being contained in any number of complex organic molecules and much simpler molecules such as carbon dioxide and methane. The atmosphere is the way by which it is transported from one place to another, here we envisage the amount of carbon in various "sinks" around the world, as well as in and above it.

Petermann Glacier, Greenland sheds a huge iceberg

There is estimated to be over 5 x 1022g of carbon on earth. One tonne is 106g, so this is 5 x 1016 tonnes, or to put it another way:

There are 50,000,000,000,000,000 tonnes of carbon on earth

About 99% of this is locked away in sedimentary rocks such as limestone and chalk (both of these are made of calcium carbonate CaCO3). This still leaves this number with 2 zeros knocked off the end, tonnes that are more mobile. This remainder can pass through the various carbon sinks and reservoirs as part of the carbon cycle and so is in some manner "available". This remaining carbon is distributed between a number of reservoirs, some living - for instance you represent a carbon reservoir approximately equivalent in size to a small bag of barbeque charcoal. Some is atmospheric, some is dissolved in water and some is buried beneath the earth.

Carbon reservoir Mass in tonnes of carbon x 109
(billions of tonnes of carbon)
% of total
Atmosphere 740.0      1.43    
Land plants 550.0      1.06    
Land animals 0.5      0.001    
Marine plants (algae) 1.5      0.003    
Marine animals 1.5      0.003    
Dead organic matter
(in soil and peat)
1600.0     3.08    
Coal 4500.0     8.67    
Oil and gas 500.0     0.96    
Dissolved in the oceans 38 000.0     73.2    
Marine sediments 6000.0     11.6    
Totals 51 893.5 100


This distribution is rather surprising at first sight, notably because there is so much carbon dioxide contained dissolved in the oceans and relatively little is contained in the atmosphere. The atmosphere however is exceptionally important in that it is the transfer medium between the other sinks and while relatively little stays in the atmosphere a great deal passes through it.

The oceans are by far the largest sink of carbon as dissolved carbon dioxide. This is medium-term storage and is in a balance with atmospheric carbon dioxide, if atmospheric carbon dioxide is removed, it will replaced by some that was dissolved in the oceans, if large amounts of carbon dioxide are released into the atmosphere, much of it will be absorbed by the oceans. The vast majority of carbon dioxide released since the start of the industrial revolution is now held dissolved in the worlds oceans if this was not the case, the atmospheric levels would have risen far more than they even have.

It is difficult to appreciate numbers like this in a relative manner by seeing them as a list, so here is another way of showing the data, numbers in billions of tonnes:


Land animals
0.5 billion tonnes of carbon

Marine plants (algae)
1.5 billion tonnes of carbon

Marine animals
1.5 billion tonnes of carbon

Oil and gas

Land plants


Dead organic matter
in soil and peat


Marine sediments

Dissolved in the oceans

Or as a bar chart:

Picture credits, copyright pictures used by permission: Rainforest - carbon sink - Ben Sutherland, used under Creative Commons 2.0 license