Over
the next three weeks, we are going to study how carbon cycles through our
ecosystem and how mankind affects this cycle. It is important that
we understand how carbon cycles through the ecosystem for two reasons.
The first of these reasons is that all organic material contains carbon.
From the smallest vitamin molecule all the way up to the long polymer chains
of proteins and DNA, carbon provides the basis of all organic compounds.
The
second reason why we need to understand the carbon cycle is because of
its effect on the physical environment. Carbon, in the form of carbon
dioxide, is released as a waste product of oxidation. This means
that it is released during the combustion of fossil fuels, as well as the
respiration of organisms. As we will see later, this can have a tremendous
effect on our climate, since carbon dioxide is a greenhouse gas.
Carbon
has two phases in the carbon cycle: gaseous and solid. Its gaseous
phase is mostly in the form of carbon dioxide, but it can also be found
in compounds like methane and carbon monoxide. Carbon dioxide can
be taken out of the atmosphere by photosynthesis in plants, which convert
the carbon into a solid form (sugars) that can be stored or put back into
the air during respiration. It can also be removed from the atmosphere
by being absorbed by water, where it becomes available to water plants
for photosynthesis as well as being available to form compounds such as
calcium carbonate (chalk) or to be put back into the atmosphere when the
water gets warmer.
As
we can see, the carbon cycle has reservoirs where it is stored as a solid.
The diagram at the right shows some of these. In a cycle that has
reached equilibrium, the rate at which carbon is removed from storage is
equal to the amount that is being taken out of the atmosphere. The
reason why many people are concerned about the carbon cycle is because
mankind's intervention has caused this system to go grossly out of equilibrium.
By burning fossil fuels, mankind has upset the balance of the cycle and
greatly increased the rate at which carbon is returning to the gaseous
phase. Is this a problem? In order to understand why it might
be a problem, we need to understand more about the properties of carbon
dioxide.
