D If humans pump enough carbon dioxide (CO 2 ) into the atmosphere, the stratocumulus clouds ( 层积云 ) could disappear, and the earth's temperature could climb sharply to heights not predicted in current climate models. It would burn the planet. That's the conclusion of a paper published in the jounal Nature Geoscience and described in detail by Natalie Wolchover for Quanta Magazine. As Wolchover explained, clouds have long been one of the great uncertainties of climate models. Computer models that easily capture ( 捕获 ) the complexity and detail of most climate systems just aren't powerful enough to predict worldwide changes in cloud behavior. But clouds are important. They reflect sunlight away from the earth's surface. And stratocumulus clouds are those white blankets you might have seen as you looked out the window of an airplane, rolling out below you and hiding the ground. Researchers suspect that certain sudden, past jumps in temperature may have been caused by changes to clouds like these. For the new research, scientists modeled just a small patch of sky using a supercomputer. They found that if carbon dioxide levels reach about 1,200 parts per million (ppm) in the atmosphere, stratocumulus clouds break up. That's a very high carbon dioxide concentration. Right now, levels have climbed past 410 ppm—a dangerous change from 280 ppm before the Industrial Revolution. But humans put more and more CO 2 into the atmosphere every year. If current trends continue, the earth could reach 1,200 ppm within 100 to 150 years. This could happen if our society doesn't follow through on any of its commitments to reduce emissions( 排放 ), Wolchover reported. And even if it does, the result would be another 8 degrees Celsius of heat added to the global average, on top of the dangerous changes already underway due to greenhouse gases. That's an enormous change, and it goes beyond predictions of worldwide ice melt and catastrophic sea-level rise. And once the stratocumulus clouds are gone, Wolchover reported, they likely wouldn't reappear until atmospheric carbon dioxide levels dropped below where they are currently. There's still some uncertainty in the data. The 1,200 ppm figure could change as scientists look into the issue further. 32. What can we learn from paragraph 2? A. Most climate systems are not complex. B. Cloud behavior is uncertain and hard to predict. C. Temperature changes affect the stratocumulus clouds. D. The stratocumulus clouds protect planes from sunlight. 33. How did the scientists study clouds in the new research? A. By measuring the sea level. B. By experimenting in a natural state. C.By comparing climate models. D. By computer modeling and analyzing. 34. What does "it" refer to in paragraph 4? A.The atmosphere. B. The earth. C. Our society. D. The result. 35. Which of the following statements would Wolchover most probably agree with? A. The effects of CO 2 emissions have been fully assessed. B. The stratocumulus clouds won't return if they are gone.. C. The breakup of stratocumulus clouds could result in catastrophes. D. Once CO 2 level reaches 1,200 ppm, stratocumulus clouds will go extinct.