Global warming is the most serious problem humanity has ever faced. There’s more hype (宣传) on this environmental issue than any

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问题     Global warming is the most serious problem humanity has ever faced. There’s more hype (宣传)  on this environmental issue than any other. In the late 1970s computer models predicted that because of the heat-trapping buildup of carbon dioxide in the atmosphere, the earth would warm up by several degrees over the next century. A lot of bad weather gets linked to global warming in the media, which regularly predict that more and fiercer hurricanes, longer droughts and more severe rainstorms will result.
    What has actually been going on? One computer model says the earth’s temperature should have already increased by an easily detectable 0.3 to 0.4 degrees Celsius since 1979. Some satellite data, however, show that the earth’s temperature has actually cooled slightly over the last 18 years.
And despite seasonal variations, the frequency of intense Atlantic hurricanes and their maximum wind speed have not increased over the past half-century.
    If climate models turn out to be correct, it may be prudent to limit carbon-dioxide emissions in the future. But many experts feel there is no need to rush into drastic action. "We have a decade or so to collect data and refine our models before we might have to act," says Jerry North, professor of meteorology at Texas A&M. There is also time for scientists to develop carbon-intensive energy technologies, which we can switch to later at a lower cost.
    "Even though it will disappoint many of you, the evidence is that you have a very bright future." This is how I finished my presentation at American University, eliciting a few chuckles from the audience.
    On a more serious note, I asked the students to consider a radical proposition: Economic growth and technological progress are not enemies of the environment but, are perhaps its best friends, since they allow us to reduce humanity’s footprint on the natural world. High-tech agriculture boosts farm productivity, which means a cheaper good supply and more land spared for nature. Better sewage treatment means that our rivers and streams can run freer of pollutants.
What has happened to the earth’s temperature over the last 18 years according to satellite data?

选项 A、It has increased slightly.
B、It has not changed.
C、It has decreased slightly.
D、It is not sure if it has changed.

答案C

解析
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