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Carbon Dioxide (CO2)
arbon dioxide is a very familiar molecule that
is the product of human respiration and of the
combustion of fossil fuels. This gas also puts the
“fizz” in soda pop. It turns out that the simple, familiar CO2 molecule has profound implications for
our continued existence on this planet.
The concentration of carbon dioxide in the
earth’s atmosphere has risen steadily since the beginning of the Industrial Revolution and is expected
to double from today’s levels in the next 50 years.
This change will have important effects on our environment. Consider the case of global warming.
Many scientists feel that the increased CO2 levels
will trap more of the sun’s energy near the earth,
significantly increasing the earth’s average temperature. Some evidence suggests that this is already
occurring, although scientists disagree about the
contribution of CO2 to the changes. One thing that
everyone does agree on is that the increased CO2
levels will make plants grow faster.
On the surface the increase in plant growth due
to increased CO2 might seem like a good thing.
Surprisingly, this situation could spell disaster for
plant eaters, from caterpillars to antelopes, and for
the animals that eat these herbivores. Faster plant
growth often leads to lower nutritional value. As the
plants increase their rate of photosynthesis and use
the carbon in CO2 to build more fiber and starch,
the amount of nitrogen—which indicates the
amount of proteins present—declines. Studies show
that new leaves on plants grown in a CO2-rich
atmosphere are starchy, but protein-poor. This is bad
news for caterpillars, which need to bulk up before
they pupate. Studies have indicated that caterpillars
eat 40% more of the starchy, protein-poor leaves but
grow 10% slower and produce smaller than normal
adult butterflies.
Studies on larger herbivores, such as cows and
sheep, have been more difficult to carry out. Nevertheless, indications are that plants grown in a
CO2-enriched environment provide less protein and
produce slower growth in these species as well.
Research is continuing to try to assess the effects
of the increasing CO2 levels on the food chain.
A Monarch butterfly caterpillar eating a leaf.