問題詳情

Scientists long believed that dependence on fossil fuels, for all its problems, would offer one enormous benefit.Carbon dioxide is also the primary fuel for plant growth. Using the energy from sunlight, they convert carbon in the airinto energy-dense compounds like glucose. All life runs on these compounds. Humans have raised the level of carbon dioxidein the atmosphere by 40 percent since the Industrial Revolution, and are on course to double or triple it this century. Studieshave long suggested that the extra gas would supercharge the world’s food crops.But many of those studies were done in artificial conditions. For the past decade, scientists at the University of Illinoishave been putting the “CO2 fertilization effect” to a real-world test. They planted soybeans in a field, then sprayed extra carbondioxide from a giant tank. They hoped the gas might bump yields as much as 30 percent. At harvest, the bump was only half aslarge. Their tests on corn, America’s most valuable crop and the basis for its meat production and its biofuel industry, were evenworse. There was no bump. Their work and that of others suggests that extra carbon dioxide does act as plant fertilizer, but thatthe benefits are probably less than needed to avert food shortages. Other recent evidence suggests that longstandingassumptions about food production on a warming planet may have been too optimistic.Two economists, Wolfram Schlenker of Columbia University in New York and Michael J. Roberts of North Carolina StateUniversity, have compared crop yields and natural temperature variability at a fine scale. Their work shows that when crops aresubjected to temperatures above a certain threshold—about 29 degrees Celsius for corn and 30 degrees Celsius forsoybeans—yields fall sharply. This suggests that in some climates, with more scorching days, some crop yields could fall by 30percent or more.A paper by David B. Lobell of Stanford University in California and Dr. Schlenker suggests that temperature increases inFrance, Russia, China and other countries are already suppressing crop yields. “I think there’s been an under-recognition of justhow sensitive crops are to heat,” Dr. Lobell said. Such research is controversial. The findings go beyond those of a 2007 reportby the United Nations’ Intergovernmental Panel on Climate Change, which found that while climate change was likely to posesevere challenges for agriculture in the tropics, it would probably be beneficial in some of the chillier regions of the NorthernHemisphere, aided by the carbon dioxide effect. At the University of Illinois, a leading scientist behind the work there, StephenP. Long, sharply criticized the report. “I felt it needed to be much more honest in saying this is our best guess at the moment,but there are probably huge errors in there,” he said.(Source: Excerpted from New York Times)
46. Which of the following statements best represents the main idea of this passage?
(A) Fossil fuels could offer enormous benefit.
(B) Carbon dioxide helps bump crop yields.
(C) Carbon dioxide affects climate change.
(D) Climate change and crop yields are closely related.
(E) Carbon dioxide effect could help chillier regions to produce more crops.

參考答案

答案：D
難度：適中0.5
統計：A(0),B(0),C(0),D(1),E(0)

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