填空题 Scientists are looking at ways to {{U}} {{U}} 1 {{/U}} {{/U}}the global temperature by removing greenhouse gases from the air. Carbon dioxide has a {{U}} {{U}} 2 {{/U}} {{/U}}effect on the Earth's temperature. Since the industrial revolution, humans have been burning {{U}} {{U}} 3 {{/U}} {{/U}}amounts of fossil fuels, releasing large amounts of carbon dioxide. The gas is changing the climate, warming the {{U}} {{U}} 4 {{/U}} {{/U}}for plants and animals and raising sea {{U}} {{U}} 5 {{/U}} {{/U}}. Even if we stopped burning fossil fuels today, there is enough carbon dioxide in the atmosphere. Hence, we have the idea of finding ways of {{U}} {{U}} 6 {{/U}} {{/U}}carbon dioxide.
In recent years there have been {{U}} {{U}} 7 {{/U}} {{/U}}to remove the carbon dioxide from its {{U}} {{U}} 8 {{/U}} {{/U}}in power plants. {{U}} {{U}} 9 {{/U}} {{/U}}have been fitted to the {{U}} {{U}} 10 {{/U}} {{/U}}, so the carbon dioxide produced during fuel burning can be removed from the {{U}} {{U}} 11 {{/U}} {{/U}}emissions. The carbon dioxide can be cooled and pumped for {{U}} {{U}} 12 {{/U}} {{/U}}in underground rock chambers, which is a useful way of preventing carbon dioxide from entering the {{U}} {{U}} 13 {{/U}} {{/U}}. But what about the {{U}} {{U}} 14 {{/U}} {{/U}}that is already out there? The problem with removing carbon dioxide from the atmosphere is that it's {{U}} {{U}} 15 {{/U}} {{/U}}at such a {{U}} {{U}} 16 {{/U}} {{/U}}concentration. Removing the gas takes lots of energy. Though it is expensive, it's {{U}} {{U}} 17 {{/U}} {{/U}}. Extracting the {{U}} {{U}} 18 {{/U}} {{/U}}of carbon dioxide in the atmosphere would require enormous volumes of {{U}} {{U}} 19 {{/U}} {{/U}}to be processed. Therefore, most scientists have {{U}} {{U}} 20 {{/U}} {{/U}}at the idea.