No Silver Lining

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GLOBAL-WARMING SCENARIOS ARE MOSTLY GLOOM and doom. As humans burn more fossil fuels, more carbon dioxide (CO2) enters the atmosphere. CO2 traps the sun's heat, causing a warmer climate, rising sea levels and drastic changes in weather. The one bright spot seemed to be that because plants "breathe" CO2, they might be expected to thrive.

Not necessarily, it turns out. A study of two artificial rain forests created inside greenhouses at the University of Basel, Switzerland, indicates that too much CO2 can harm plants. One greenhouse had an atmosphere like today's; the second had as much CO2 as is predicted for the middle of the next century. The effects: plants in the second rain forest produced starch deposits that could interfere with photosynthesis, and the soils they lived in showed a rapid loss of nutrients. The scientists are now working with other experimental ecologies, and the preliminary results are the same.