二氧化碳排放增多 降低植物的调节气温作用
文章来源:未知 文章作者:meng 发布时间:2010-05-04 01:05 字体: [ ]  进入论坛
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Trees and other plants help keep the planet cool, but rising levels of carbon dioxide in the atmosphere are turning down this global air conditioner. According to a new study by researchers at the Carnegie Institution for Science, in some regions more than a quarter of the warming from increased carbon dioxide is due to its direct impact on vegetation(植物,草木) . This warming is in addition to(除……之外) carbon dioxide's better-known effect as a heat-trapping greenhouse gas. For scientists trying to predict global climate change in the coming century, the study underscores the importance of including plants in their climate models. "Plants have a very complex and diverse influence on the climate system," says study co-author Ken1 Caldeira of Carnegie's Department of Global Ecology. "Plants take carbon dioxide out of the atmosphere, but they also have other effects, such as changing the amount of evaporation2(蒸发) from the land surface. It's impossible to make good climate predictions without taking all of these factors into account."

Plants give off(发出)water through tiny pores in their leaves, a process called evapotranspiration(蒸发蒸腾) that cools the plant, just as perspiration3(汗水,流汗) cools our bodies. On a hot day, a tree can release tens of gallons of water into the air, acting4 as a natural air conditioner for its surroundings. The plants absorb carbon dioxide for photosynthesis5(光合作用) through the same pores (called stomata气孔). But when carbon dioxide levels are high, the leaf pores shrink. This causes less water to be released, diminishing the tree's cooling power.

The warming effects of carbon dioxide as a greenhouse gas have been known for a long time, says Caldeira. But he and fellow Carnegie scientist Long Cao were concerned that it is not as widely recognized that carbon dioxide also warms our planet by its direct effects on plants. Previous work by Carnegie's Chris Field and Joe Berry had indicated that the effects were important. "There is no longer any doubt that carbon dioxide decreases evaporative cooling by plants and that this decreased cooling adds to global warming," says Cao. "This effect would cause significant warming even if carbon dioxide were not a greenhouse gas."

In their model, the researchers doubled the concentration of atmospheric6 carbon dioxide and recorded the magnitude(大小,量级) and geographic7 pattern of warming from different factors. They found that, averaged over the entire globe, the evapotranspiration effects of plants account for 16% of warming of the land surface, with greenhouse effects accounting8 for the rest. But in some regions, such as parts of North America and eastern Asia, it can be more than 25% of the total warming. "If we think of a doubling of carbon dioxide as causing about four degrees of warming, in many places three of those degrees are coming from the effect of carbon dioxide in the atmosphere, and one is coming from the direct effect of carbon dioxide on plants."

The researchers also found that their model predicted that high carbon dioxide will increase the runoff from the land surface in most areas, because more water from precipitation(坠落,沉淀) bypasses the plant cooling system and flows directly to rivers and streams. Earlier models based on greenhouse effects of carbon dioxide had also predicted higher runoff, but the new research predicts that changes in evapotranspiration due to high carbon dioxide could have an even stronger impact on water resources than those models predict.

"These results really show that how plants respond to carbon dioxide is very important for making good climate predictions," says Caldeira. "So if we want to improve climate predictions, we need to improve the representation of land plants in the climate models. More broadly, it shows that the kind of vegetation that's on the surface of our planet and what that vegetation is doing is very important in determining our climate. We need to take great care in considering what kind of changes we make to forests and other ecosystems9(生态系统) , because they are likely to have important climate consequences."

The study is published in the May 3-7 online edition of the Proceedings10 of the National Academy of Sciences.



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1 ken k3WxV     
n.视野,知识领域
参考例句:
  • Such things are beyond my ken.我可不懂这些事。
  • Abstract words are beyond the ken of children.抽象的言辞超出小孩所理解的范围.
2 evaporation Pnoxc     
n.蒸发,消失
参考例句:
  • Be careful not to lose too much liquid by evaporation.小心不要因蒸发失去太多水分。
  • Our bodies can sweat,thereby losing heat by evaporation.我们的身体能出汗,由此可以蒸发散热。
3 perspiration c3UzD     
n.汗水;出汗
参考例句:
  • It is so hot that my clothes are wet with perspiration.天太热了,我的衣服被汗水湿透了。
  • The perspiration was running down my back.汗从我背上淌下来。
4 acting czRzoc     
n.演戏,行为,假装;adj.代理的,临时的,演出用的
参考例句:
  • Ignore her,she's just acting.别理她,她只是假装的。
  • During the seventies,her acting career was in eclipse.在七十年代,她的表演生涯黯然失色。
5 photosynthesis A2Czp     
n.光合作用
参考例句:
  • In apple trees photosynthesis occurs almost exclusively in the leaves.苹果树的光合作用几乎只发生在叶内。
  • Chloroplasts are the structures in which photosynthesis happens.叶绿体就是光合作用发生的地方。
6 atmospheric 6eayR     
adj.大气的,空气的;大气层的;大气所引起的
参考例句:
  • Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
  • Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。
7 geographic tgsxb     
adj.地理学的,地理的
参考例句:
  • The city's success owes much to its geographic position. 这座城市的成功很大程度上归功于它的地理位置。 来自《简明英汉词典》
  • Environmental problems pay no heed to these geographic lines. 环境问题并不理会这些地理界限。 来自英汉非文学 - 环境法 - 环境法
8 accounting nzSzsY     
n.会计,会计学,借贷对照表
参考例句:
  • A job fell vacant in the accounting department.财会部出现了一个空缺。
  • There's an accounting error in this entry.这笔账目里有差错。
9 ecosystems 94cb0e40a815bea1157ac8aab9a5380d     
n.生态系统( ecosystem的名词复数 )
参考例句:
  • There are highly sensitive and delicately balanced ecosystems in the forest. 森林里有高度敏感、灵敏平衡的各种生态系统。 来自《简明英汉词典》
  • Madagascar's ecosystems range from rainforest to semi-desert. 马达加斯加生态系统类型多样,从雨林到半荒漠等不一而足。 来自辞典例句
10 proceedings Wk2zvX     
n.进程,过程,议程;诉讼(程序);公报
参考例句:
  • He was released on bail pending committal proceedings. 他交保获释正在候审。
  • to initiate legal proceedings against sb 对某人提起诉讼
TAG标签: climate carbon plants air
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