Passage Three
Add CO2 to the atmosphere, and the climate will get warmer - that much is well established. But climate change and carbon aren't in a one-to-one relationship. If they were, climate modeling would be a cinch. How much the globe will warm if we put a certain amount of CO2 into the air depends on the sensitivity of the climate. How vulnerable is the polar sea ice; how rapidly might the Amazon dry up; how fast could the Greenland ice cap disintegrate? That’s why models like those from the Intergovernmental Panel on Climate Change spit out a range of predictions for future warming, rather than a single neat number.
One of the biggest questions in climate sensitivity has been the role of low-level cloud cover. Low-altitude clouds reflect some of the sun's radiation back into the atmosphere, cooling the earth. It's not yet known whether global warming will dissipate clouds, which would effectively speed up the process of climate change, or increase cloud cover, which would slow it down.
But a new study published in the July 24 issue of Science is clearing the haze. A group of researchers from the University of Miami studied cloud data of the northeast Pacific Ocean over the past 50 years and combined that with climate models. They found that low-level clouds tend to dissipate as the ocean warms - which means a warmer world could well have less cloud cover. “That would create positive feedback, a reinforcing cycle that continues to warm the climate,” says Amy Clement, the leading author of the Science study.
The data showed that as the Pacific Ocean has warmed over the past several decades - part of the gradual process of global warming-low-level cloud cover has lessened. That might be due to the fact that as the earth's surface warms, the atmosphere becomes more unstable and draws up water vapor from low altitudes to form deep clouds high in the sky. (Those types of high - altitude clouds don’t have the same cooling effect.) The Science study also found that as the oceans warmed, the trade winds - the easterly surface winds that blow near the equator - weakened, which further dissipated the low clouds. The question now is whether this process will continue in the future, as the world keeps warming.
Questions 11-15 are based on Passage Three.
11. We can learn from paragraph one that climate models ______.
A. can only give a broad picture instead of detailed data
B. become easier to establish with current technology
C. leave much for improvement in terms of accuracy
D. fail to predict some climate changes
12. What is true of low-level cloud cover according to the passage?
A. It is rather sensitive to temperature changes.
B. It has a cooling effect on the earth surface.
C. It functions more effectively in warmer areas.
D. It is more often than not neglected in climate modeling.
13. The word “haze” in paragraph three is closest in meaning to ______.
A. mist
B. puzzle
C. solution
D. misunderstanding
14. “Positive feedback” in paragraph three refers to ______.
A. predictable climate patterns relating to calculable cloud volume
B. the thickening cloud cover, cooling down the earth surface
C. the reinforcing effect of cooler cloud temperature on regional climate
D. a warmer climate resulting in less cloud cover, which in turn warms the climate
15. The lessening of low-level cloud cover over the Pacific Ocean may be caused by ______.
A. more trade winds in this region
B. the climate change around the equator
C. less water vapor at low altitude
D. the unstable air pressure over the ocean
