[题目]Scientists in the United States say plant life has increased on Earth in the past twenty years and that in every area of plant growth the increase is the result of weather conditions. Eight scient 题目和参考答案——青夏教育精英家教网—

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【题目】Scientists in the United States say plant life has increased on Earth in the past twenty years and that in every area of plant growth the increase is the result of weather conditions.

Eight scientists from across the United States did the study. The space agency NASA and the Department of Energy paid for it. The findings were published in the magazine Science.

The researchers spent one and a half years examining weather satellite information. The information was recorded from 1982 to 1999. That period was one of the warmest on record. Researchers found that rainfall generally increased during that time.

The satellites measured the number of leaves on plants and the amount of sunlight taken in. The scientists used that information to estimate what is called net primary production. This is the total amount of carbon stored in land plants.

The scientists report a 6% increase in stored carbon since 1982. They say gains were high in equatorial areas, especially around the Amazon River in South America. The area alone had a 1 % increase in the net primary production.

The study was led by Ramakrishna Nemani of the University of Montana in Missoula. He says reduced cloud cover led to the growth in Amazon area. He also says the lack of clouds allowed more sunlight to get through. More sunlight meant increases in photosynthesis(光合作用）. That is the process by which plants use energy from sunlight to produce the chemicals they need to grow.

Northern Canada, the north-central United States and northern Europe were second in increased plant growth. Ramakrishna Nemani says a rise in temperature helped plants there.

All together, the report says 25% of areas of plant life on Earth experienced increases. But the scientists also note the increase in the number of people on Earth and carbon dioxide levels in the atmosphere. Ranga Myneni of Boston University in Massachusetts, another study scientist says humans use about half the net primary production on Earth. And he notes that the world population grew by 36% during the period of time studied.