Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 21 to 27.Most scientists agree that global warming presents the greatest threat to the environment. There is little doubt that the Earth is getting warmer. In the last century the average temperature rose about 0.6 degrees C around the world. Many experts warn that global warming will cause sea levels to rise dramatically. In the past 100 years the oceans have risen 10 to 20 cms- but that's nothing compared to what would happen if, for example, Greenland's massive ice sheet were to melt.Just as the evidence is clear that temperatures have risen in the last century, it's also well established that carbon dioxide in the Earth's atmosphere has increased about 30 percent, allowing the atmosphere to trap too much heat. However, the exact link, if any, between the increase in carbon dioxide emissions and the higher temperatures is still being disputed. Most scientists believe that humans, by burning fossil fuels such as coal and petroleum, are largely to blame for the increase in carbon dioxide. But some scientists also point to natural causes, such as volcanic activity.The current rate of warming is faster than ever before, however, which suggests it probably is not a natural occurrence. And a large number of scientists believe the rise in temperatures will, in fact, speed up. A recent study suggested that Greenland's ice sheet will begin to melt if the temperature there rises by three degrees C. That is something many scientists think is likely to happen in another hundred years. The complete melting of the Greenland ice cap would raise sea levels by seven metres. Even a partial melting would cause a one-metre rise. Such a rise would have a devastating impact on low-lying islands, such as the Maldives, which would be entirely submerged.Other scientists emphasise that such doomsday scenarios may be hundreds of years in the future. 'You can't say with any certainty that sea-level rises are going to have a huge impact on society,' says Stouffer. 'Who knows what the planet will look like 5000 years from now?' Most climate scientists, however, agree that global warming is a threat that has gone unchecked for too long. 'Is society aware of the seriousness of climate warming? I don't think so,' says Marianne Douglas, professor of geology at the University of Toronto. 'Otherwise we'd all be leading our lives differently. We'd see a society that used alternative sources of energy, with less dependence on fossil fuels.'(Adapted from Objective for IELTS by Michael Black and Wendy Sharp)Câu 21. Which best serves as the title for the passage?

Câu hỏi: Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 21 to 27.Most scientists agree that global warming presents the greatest threat to the environment. There is little doubt that the Earth is getting warmer. In the last century the average temperature rose about 0.6 degrees C around the world. Many experts warn that global warming will cause sea levels to rise dramatically. In the past 100 years the oceans have risen 10 to 20 cms- but that's nothing compared to what would happen if, for example, Greenland's massive ice sheet were to melt.Just as the evidence is clear that temperatures have risen in the last century, it's also well established that carbon dioxide in the Earth's atmosphere has increased about 30 percent, allowing the atmosphere to trap too much heat. However, the exact link, if any, between the increase in carbon dioxide emissions and the higher temperatures is still being disputed. Most scientists believe that humans, by burning fossil fuels such as coal and petroleum, are largely to blame for the increase in carbon dioxide. But some scientists also point to natural causes, such as volcanic activity.The current rate of warming is faster than ever before, however, which suggests it probably is not a natural occurrence. And a large number of scientists believe the rise in temperatures will, in fact, speed up. A recent study suggested that Greenland's ice sheet will begin to melt if the temperature there rises by three degrees C. That is something many scientists think is likely to happen in another hundred years. The complete melting of the Greenland ice cap would raise sea levels by seven metres. Even a partial melting would cause a one-metre rise. Such a rise would have a devastating impact on low-lying islands, such as the Maldives, which would be entirely submerged.Other scientists emphasise that such doomsday scenarios may be hundreds of years in the future. 'You can't say with any certainty that sea-level rises are going to have a huge impact on society,' says Stouffer. 'Who knows what the planet will look like 5000 years from now?' Most climate scientists, however, agree that global warming is a threat that has gone unchecked for too long. 'Is society aware of the seriousness of climate warming? I don't think so,' says Marianne Douglas, professor of geology at the University of Toronto. 'Otherwise we'd all be leading our lives differently. We'd see a society that used alternative sources of energy, with less dependence on fossil fuels.'(Adapted from Objective for IELTS by Michael Black and Wendy Sharp)Câu 21. Which best serves as the title for the passage?