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SAT Reading Post-Test

SAT Reading Test:

Carbon Dioxide Passage

The concentration of carbon dioxide in our
atmosphere has been steadily increasing since
about 1750. Carbon dioxide lets in sun energy and
then traps it as heat energy, so the more carbon
05dioxide in the atmosphere, the higher the average
global temperature. Scientists are concerned that
even slight increases in global temperatures will
significantly affect plant and animal life on Earth.


In the past, photosynthesis has been able to keep
10the level of carbon dioxide in the air at a lower
level. Plants and algae convert water and carbon
dioxide into oxygen and glucose, using the sun's
energy. Carbon from carbon dioxide becomes
trapped or "fixed" as the plant uses glucose to build
15cellulose and starches, which make up most of the
plant's structure.


Human industry is the main cause of increased
carbon dioxide in the atmosphere. Cutting down
forests to make room for expanding cities or farm-
20land reduces the amount of carbon dioxide being
removed. The wood is also often burned, releasing
more carbon dioxide into the air. Burning fossil
fuels for energy releases even more carbon dioxide
that had previously been locked up in the coal, oil,
25or gas underground.


We can reduce the amount of carbon dioxide by
reducing how much we release, either by burning
fewer fossil fuels or by removing carbon dioxide as
the fuel is being burned. We can burn fewer fossil
30fuels by switching to other forms of power that
don't release carbon dioxide, such as solar or wind
power, but these methods are more expensive. We
can "scrub" the carbon dioxide from the air at the
power plant where the fuel is burned, but that is also
35expensive. It is also does not work for the carbon
dioxide produced by cars, trucks, and airplanes.
Reducing our output of carbon dioxide, though
a commendable idea, may not reduce the levels
enough to have a meaningful impact. We might
40need to go one step farther and try to remove car-
bon dioxide from the air.


Many research and development companies are
now developing systems that will act like artificial
"trees" and remove carbon dioxide from the atmos-
45phere. Several built their approach on a method
used in submarines and space vehicles. They com-
bine the carbon dioxide with a strong base called
sodium hydroxide to produce sodium bicarbonate,
also known as baking soda. Bubbling air through
50a solution of sodium hydroxide works well enough
for the small amount of air in a space vehicle or
submarine, but this would be a slow way to process
a large amount of air.


One researcher found a way to make a plastic
55with hydroxide components that would remove
carbon dioxide from air as it passes over the surface
of the plastic. Filters made out of long strands of
this plastic can then remove carbon dioxide as
wind pushes the air through the strands. The filters,
60therefore, act much like leaves in a tree.


This plastic is inexpensive, but making it into
filters, building towers that contain many "leaves"
of the filters, and processing the plastic to remove
the carbon dioxide so the plastic can be reused is
65currently very expensive. To pay for the cost, gasoline
would end up increasing in price. If manufacturers
could get the cost of this method down to $100 per
metric ton of carbon dioxide removed, for example,
the price of gas would still have to increase by
70about 88 cents to cover the cost. Researchers are
optimistic that they could actually get the cost down
to $25 per metric ton. If they achieve this goal, we
someday may see artificial trees in our cities, assisting
the real trees in cleaning the air.