El Nino—the periodic warming of eastern Pacific Ocean waters—causes a burst of plant growth throughout the world, and this removes carbon dioxide from the atmosphere, researchers have found.
(112) The new study shows that natural weather events such as the brief warming caused by El Nino, have a much more dramatic effect than previously believed on how much carbon dioxide is absorbed by plants and how much of the gas is expelled by the soil.
Atmospheric carbon dioxide, or CO2, has been increasing steadily for decades. This is thought to be caused by an expanded use of fossil fuels and by toppling of tropical forests. Scientists have linked the CO2 rise to global warming, a phenomenon known as the greenhouse effect. (113) Alarmed nations of the world now are drawing up new conservation policies to reduce fossil fuel burning, in hopes of reducing greenhouse gases in the atmosphere.
But David Schimel of the National Center for Atmospheric Research, a co-author of the new study, says that before determining how much to reduce fossil fuel burning we should consider the effects of natural climate variations on the ability of plants to absorb CO2.
Schimel said satellite measurements of CO2, plant growth and temperature show that natural warming events such as El Nifio at first cause more CO2 to be released into the atmosphere, probably as the result of accelerated decay of dead plant matter in the soil. But later, within two years, there is an explosion of growth-in forests and grasslands, which means plants suck more carbon dioxide out of the atmosphere.
"We think that there is a delayed response in vegetation and soil to the warming effects of such phenomena as El Nifio, and this leads to increased plant growth," said Schimel.
(114) However, be said, it is not clear whether the warming by El Nino causes a net decrease in the buildup of CO2 over the long haul. "We don't really know that yet," said Schimel. What the study does show, however, is that the rise and fall of CO2 in the atmosphere is strongly influenced by natural changes in global temperature, said B. H. Braswell of the University of New Hampshire, another co-author of the study.
Braswell said that in years when the global weather is cooler than normal, there is a decrease in both the decay of dead plants and in new plant growth. This causes an effect that is the opposite of El Nino warming: CO2 atmosphere levels first decline and later increase.
(115) "I think we have demonstrated that the ecosystem has a lot more to do with climate change than was previously believed," said Braswell, "Focusing on the role of human activity in climate change is important, but man made factors are not the only factors."
(81)
第1题
The first paragraph mainly discusses______.
A.the features of the computer age
B.the phenomenon of quantification
C.the mutual influence between computers and human
D.the change in the working modes of human minds
第2题
The example of a bird sleeping in front of a mirror indicates that _________.
A.the phenomenon of birds dozing in pairs is widespread
B.Birds prefer to sleep in pairs for the sake of security
C.even an imagined companion gives the bird a sense of security
D.a single pet bird enjoys seeing its own reflection in the mirror
第4题
A.temperate
B.subtropical
C.humid
D.continental
第5题
A.Reef corals.
B.Bears.
C.Penguins.
D.Camels.
第6题
Paragraphs 2 and 3 are written to
A.discuss the causes of climatic irregularities.
B.exemplify the abnormal effects of EI Nino.
C.explain the way in which EI Nino develops.
D.show the recent observations of scientists.
第7题
Scientists believe that human evolution______.
A.has seldom been accompanied by climatic changes
B.has exerted little influence on climatic changes
C.has largely been effected by climatic changes
D.has had a major impact on climatic changes
第8题
5:Scientists believe that human evolution ______.
A.has seldom been accompanied by climatic changes
B.has exerted little influence on climatic changes
C.has largely been effected by climatic changes
D.has had a major impact on climatic changes
第9题
Scientists believe that human evolution_.
A. has seldom been accompanied by climatic changes
B. has exerted little influence on climatic changes
C. has largely been effected by climatic changes
D. has had a major impact on climatic changes
第10题
A.Reef corals.
B.Penguins.
C.Bears.
D.Camels.
为了保护您的账号安全,请在“上学吧”公众号进行验证,点击“官网服务”-“账号验证”后输入验证码“”完成验证,验证成功后方可继续查看答案!