Movingflight times from night to day could reduce air travel's contributions to -组卷网

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Moving flight times from night to day could reduce air travel's contributions to global warming, a new study suggests. Scheduling more (laytime flights may reduce the influence of contrails ——the visible lines of white steam that many planes leave behind them in the sky.

The role of contrails in climate change is still being studied, but some scientists believe they contribute to the greenhouse effect by trapping heat in the atmosphere.

Nicola Stuber, first author of the study, suggests that contrails' overall impact on climate change is almost as big as that of aircraft^? s carbon dioxide emissions (排放)over a hundred-year period. Aircraft are believed to be responsible for 2-3% of human carbon dioxide emissions. Like other high, thin clouds, contrails reflect sunlight back into space and cool the planet. However, they also trap energy in the atmosphere and increase the warming effect.

Stuber and other scientists believe that the effect of the contrails is big. " On average, the green-house effect controls the effects of contrails,said Stuber, a meteorologist at England's University of Reading. "The warming effect is far greater for contrails left by night flights," Stuber added. "The cooling effect only happens (luring the day when the sun is up. During the night the greenhouse warming is no longer balanced and that is why the contribution of night-flight is so large."

Most commercial airline traffic occurs during daylight hours. For example, only one in four United Kingdom flights is a night flight, but those flights create some 60% of the warming created by contrails, the study reports.

【小题1】How do contrails increase the greenhouse effect?

A．They give off heat.

B．They absorb daylight.

C．They trap heat in the atmosphere.

D．They reflect sunlight back into space.

【小题2】What does the underlined word "they" in Paragraph 3 refer to?