根据短文内容,从下框的A～F选项中选出能概括每一段主题的最佳选项,选项中有一项为多余项.
A. The likely reason of global warming
B．Global warming-a world problem
C．The fast increase in recent years
D．What we should do to avoid greenhouse gases producing
E．The earth is becoming warmer
F．Different opinions on the cause of global warming
1________
Is the world warming up? According to many reports, the answer is yes. Eleven of the hottest years
since 1850 appeared between 1995 and 2006. Last year, the United Nation's Intergovernment Panel on
Climate Change (IPCC) reported the earth was about 0.75 ? warmer than it was in 1850. While this
doesn't sound like a lot, a small difference in average temperature can make a big difference in climate.
During the last Ice Age, the planet was only about five degrees colder than now.
2．________
It's all about the speed at which temperatures are changing. In the past,temperatures moved up or down step by step. But in the 20th century, especially since 1976, temperatures have likely risen more quickly
than during any century in the last 1000 years. Warming may bring improved harvests to northern countries such as Canada and Russia. However, many species won't like these conditions. They begin moving
towards cooler places and cause lots of trouble to human world.
3．________
The IPCC reported that human activity is very likely responsible for increasing the greenhouse effect.
Some gases cause the air to take in heat energy. Without the greenhouse effect, the earth's average
temperature would be－18? rather than the present comfortable 14.6 ?. The main greenhouse gases are
carbon dioxide, water vapor and some other gases. Burning oil,coal and waste add to the carbon dioxide,
and it has increased 35% since 1850.
4．________
Many researchers have found that natural forces alone don't explain the temperature increases over the
last 30 to 40 years. Their study shows that as carbon dioxide goes up, temperature will rise, too. But some scientists don't agree. They think the effect of human produced greenhouse gases is very small compared
to the normal changes that the climate causes.
5．________
When asked whether humans are causing the world warming,Carl Wunsch, a professor at Massachusetts Institute of Technology says, "It seems very likely from what I've seen. Is it 100% sure? No. There is
something to do with natural changes." Does that mean we should have a "waitandsee" attitude? No. He
points out we buy house insurance not because we are sure our homes will be on fire, but because it's a
danger we'd rather avoid.
