Energy and Changes in the Environment - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 51

and the animals they nourish die, their remains mostly decay before they
have a chance to sink. The carbon dioxide from the decaying nourishes
new plants, reducing the need for more carbon from the atmosphere.
CARBON DIOXIDE CONCENTRATION
The concentration of carbon dioxide in the atmosphere is about 360
parts per million. Some believe this could increase another 200 to 600 ppm
by the end of the century. It may have been over 300 ppm more than 400,000
years ago with lows around 200 ppm at 350,000, 200, 000 and 30,000 years
ago. Between these lows were peaks of 250 to 270 ppm.
The present levels may depend on population, capita consumption
of fossil fuel, deforestation and aforestation activities.
The faster the climate warms up, the more likely it is that feedback
processes will change the greenhouse gas buildup. There are many that
believe that CO 2 and other trace greenhouse gases could double sometime
within the next century.
Estimates on fossil fuel growth indicate a 1-2% annual growth rate.
This could double the amount CO 2 based on preindustrial levels.
The different greenhouse gases can have complicated interactions.
Carbon dioxide may cool the stratosphere which slows the process that
destroys ozone. Stratospheric cooling can also create high altitude clouds
which interact with chlorofluorocarbons to destroy ozone. Methane
may be produced or destroyed in the lower atmosphere at various rates,
which depend on the pollutants that are present. Methane can also affect
chemicals that control ozone formation.
In the exchange and distribution of carbon, an important process is
the uptake by green plants. Since CO 2 is the basis of photosynthesis and
more CO 2 in the air means faster rates of photosynthesis. Other factors
are the amount of forested and planted areas, and the effects of climate
change on ecosystems.
The removal of CO 2 from the atmosphere takes place through
biological and chemical processes in the oceans, which may take decades
or centuries. Climate changes modify the mixing processes in the oceans.
About the same amount of carbon (almost 800 billion tons) is stored
in the atmosphere as is stored in living plant matter on land, mostly in
trees. Animals retain a small amount of carbon about 1-2 billion tons and
the amount in humans is just a small percentage of this. Bacteria have