3、Scientists have long believed one way to stop the
Earth’s atmosphere from warming is by planting more
trees. The idea is that more trees take in or absorb some of the carbon dioxide
in the atmosphere. Carbon dioxide is a gas released by cars, factories and
other human activities. The gas traps heat in the Earth’s atmosphere, which warms the planet. However, two new studies have
found that trees may not be as helpful in reducing carbon dioxide as had been
thought.
The first study was done at Duke
University in Durham, North Carolina. Researchers pumped extra carbon dioxide
into a test area where pine trees were growing. The trees grew thirty-four
percent faster during the first three years. However, in time, the trees slowed
to about their normal growth rate. The scientists say this is because trees
need other nutrients, such as nitrogen.
In the second study, researchers
from Duke and Bowdoin College in Brunswick, Maine examined the soil around
trees. They discovered that as the leaves broke down into the soil, all the
carbon was not trapped in the soil. Much of it was released into the atmosphere
as carbon dioxide.
Forest planting has been a part of
negotiations on a world agreement to reduce greenhouse gases that scientists
believe cause global warming. The United States, Canada, Japan and some other
industrial countries have supported the idea. But this new research suggests
the idea is not as effective as environmental activists had thought. Scientist
Ram Oren of Duke University led the study on tree growth. He says that earlier
estimates on the ability of forests to absorb carbon dioxide were overly
hopeful.
Some scientists not involved in
the studies say the research provides some of the first evidence on how trees
react to carbon dioxide. Other scientists say the research disputes(对……质疑) a belief among some coal and
power companies. The companies say that rising levels of carbon dioxide in the
atmosphere will not create harmful global warming. Instead, they say it
will increase forests and other plants.
1.What is the purpose of this passage?
A.Introduce some new ideas about the relationship
between trees and carbon dioxide.
B.Introduce recent condition of global
industrial pollution.
C.Call on people to plant more trees
to reduce greenhouse gases.
D.Point out that power companies
should be responsible for the rising levels of carbon
dioxide.
2.Why did the researchers do the TWO studies?
A.To prove that trees may not be as helpful in reducing
carbon dioxide as had been thought.
B.To get more oxygen from these trees.
C.To evaluate(评价,评估)the maximum
carbon dioxide the trees can absorb
D.To see the growth rate of these trees.
3.What happened to the leaves falling from the trees in
the second study?
A.They broke down and the main parts turned into
oxygen.
B.They broke down and the carbon
content had mainly turned into carbon dioxide.?
C.They broke down and the carbon dioxide content was
mainly absorbed in the soil.
D.They absorbed more carbon dioxide.?
4.Scientist Ram Oren is for the opinion that common
beliefs of the tree’s ability to absorb carbon dioxide
are .
A.based
B.insightful
C.overoptimistic D.totally wrong
5.The word “it” in the last paragraph probably refers to
.
A.carbon
dioxide B.nitrogen
C.atmosphere
D.coal