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 programme there is successful and the dust supply reduced, the net result may be that less carbon dioxide gets locked away in the ocean.

　　Andy, an environmental scientist has spent the past few years studying dust and says his work shows clearly the complexity of the system.For this reason the need is to focus on cutting carbon dioxide giving off rather than doing anything else.

　　Robert, an American scientist, has shown that when native grassland areas are invaded 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 grass, so less carbon goes directly into the soil from trees.” said Robert.

　　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 fight against 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.

　　36．People usually hold the opinion that________.

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