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 soaking up 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. The dust fuels oceanic life.

　　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 Ridgwell, an environmental scientist from the University of East Anglia, has spent the past few years studying dust and says his work “shows clearly that the complexity of the system and the importance of not tinkering(粗劣地修补) with it without understanding the results. For this reason the need is to focus(集中) on cutting carbon dioxide giving off rather than monkeying (瞎弄) about with the land surface.”

　　An American scientist, Robert Jackson, has shown that when native grassland areas are invaded(侵入) 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, ” says Jackson.

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