London: What could possibly he wrong with planting trees? The benefits are obvious: they firm the soil, absorb extra water and take carbon dioxide out of the atmosphere.
However, it now turns out that planting trees could add to global warming. Tree roots do a great job of keeping soil firmly on the ground and out of the wind's power. The problem is that some of those dust clouds play an important part in taking in carbon dioxide.
Huge dust storms blow out over the oceans from dry parts of North Africa and central Asia. Tons of dust are lifted and left as a thin film over the ocean surface.
Dust from China is carried east and left in the Pacific Ocean. If a tree-planting program there is successful and the dust supply reduced, the final result may be that less carbon dioxide gets locked away in the ocean.
Andy Ridgwell, an environmental scientist from the University of East Anglia, has spent the past few years studying dust and says his work shows clearly the complexity of the system and the importance of not working uselessly with it without understanding the results. For this reason the need is to focus on cutting carbon dioxide giving off rather than dealing with the land surface aimlessly.
An American scientist, Robert Jackson, has shown that when native grassland areas are occupied by trees, carbon is lost from the soil. "We are studying why the soil carbon disappears, but one theory is that trees do a lot more of their growing above ground compared to grasses, so less carbon goes directly into the soil from trees. " said Jackson.
In wet areas of the world, the gain from trees absorbing carbon dioxide above ground seems to be outweighed by the loss of carbon from the soil below ground.
Countries that plan to combat global warming by planting trees may have to think again. Solutions to environmental problems are often more complex than they first appear, and understanding the Earth's climate is a very great challenge.
64. People usually hold the opinion that _______.
A. huge dust storms can destroy carbon dioxide
B. huge dust storms can destroy the oceans on the earth
C. planting trees could reduce global warming
D. planting trees is the only way to control huge dust storms
65. Andy Ridgwell, the environmental scientist, believes that _______.
A. environmental problems are more complex than expected
B. trees shouldn't have been planted in dry places
C. dust plays a more important part than trees
D. carbon dioxide is harmful to everything
66. Robert Jackson's experiment proves that _______.
A. carbon can turn grass into dust
B. trees hold more carbon than grass
C. less carbon can make trees grow faster
D. grassland areas should be covered by forests
67. The underlined word "combat" in the last paragraph means _______.
A. learn about        B. give up              C. live with          D. fight against

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