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Last, and most
important to us, we come to the carbon cycle on land.
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Here we see more
detail on the fate of the 120 billion tonnes of carbon absorbed annually from
the atmosphere by plants to produce food for all.
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Half of this
food is almost immediately used by the plants themselves, returning carbon
dioxide to the atmosphere. Nearly another half (55 billion tonnes carbon) is
co-opted by animals – of many sorts - and ultimately returned to the
atmosphere as carbon dioxide. Some 4 billion tonnes is consumed by fires.
That leaves about 1 billion tonnes to be incorporated into soil or dissolved
in water and washed down rivers to the ocean.
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Now – let’s
recall that overhead which deemed the 120 billion tonnes of plant carbon
cycling as “natural”. What happened to
all the plants that are under human control? Is that not a human perturbation
too?
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Humans control a
major part of earth’s vegetation. Indeed estimates suggest humans have
cultivated 10 to 15% of the land surface. We can bet we have generally chosen
the most productive land too. We also influence the carbon cycle through our
use of forests.
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