C

　　“Plants were expected to get larger with increased carbon dioxide in the atmosphere, but changes in temperature, humidity and nutrient availability seem to have trumped the benefits of increased carbon dioxide，” said researchers from the National University of Singapore.

　　45 percent of the species studied now reach smaller adult sizes than they did in the past. The researchers pointed out that warmer temperatures and changing habitats, caused by climate change, are possible reasons for shrinking creatures.

　　“We do not yet know the mechanisms involved, or why some organism are getting smaller while others are unaffected，” the researchers said. “Until we understand more, we could be risking negative consequences that we can't yet quantify.”

　　The change was big in cold­blooded animals. Only two decades of warmer temperatures were enough to make reptiles (爬行动物) smaller. An increase of 1 degree centigrade caused nearly a 10 percent increase in metabolism (新陈代谢). Greater use of energy resulted in tiny tortoises and little lizards. Fish are smaller now too. Though overfishing has played a part in reducing numbers, experiments show that warmer temperatures also stop fish growth. There is a recent report on warmer temperatures' negative effects on plankton (浮游生物), the base of the marine ecosystem.

　　Warm­blooded animals weren't immune from the size change caused by climate change. Many birds are now smaller. Mammals have been miniaturized too. Soay sheep are thinner. Red deer are weaker. And polar bears are smaller, compared with historical records. This is not the first time this has happened in Earth's history.

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