填空题 About {{U}} {{U}} 1 {{/U}} {{/U}}years ago, Earth entered the latest interglacial period. The {{U}} {{U}} 2 {{/U}} {{/U}}pattern for an interglacial period is that there is the most carbon dioxide and methane gas which are greenhouse gases. And then the concentration of greenhouse gases gradually goes down. Now, the climate continues to warm for a while because there is a {{U}} {{U}} 3 {{/U}} {{/U}}effect. But gradually as the concentration of greenhouse gases goes down, Earth starts to cool again, and eventually you {{U}} {{U}} 4 {{/U}} {{/U}}back into an Ice Age. In the latest interglacial period, this pattern did not {{U}} {{U}} 5 {{/U}} {{/U}}now. What was different about this period than the other ones? One big {{U}} {{U}} 6 {{/U}} {{/U}}is human activity. the agricultural revolution—people began {{U}} {{U}} 7 {{/U}} {{/U}}crops and animals for food instead of {{U}} {{U}} 8 {{/U}} {{/U}}for them.
Some climate {{U}} {{U}} 9 {{/U}} {{/U}}propose that perhaps humanity was having an effect on the climate since the agricultural revolution. When you grow crops and {{U}} {{U}} 10 {{/U}} {{/U}}animals, you cut down the {{U}} {{U}} 11 {{/U}} {{/U}}, you end up with much more carbon in the atmosphere. Methane forms in large concentration above {{U}} {{U}} 12 {{/U}} {{/U}}, which increases its amount in the atmosphere. So agriculture could have a {{U}} {{U}} 13 {{/U}} {{/U}}effect on the {{U}} {{U}} 14 {{/U}} {{/U}}of Earth's atmosphere. The agricultural revolution was {{U}} {{U}} 15 {{/U}} {{/U}}by {{U}} {{U}} 16 {{/U}} {{/U}}an Ice Age. But {{U}} {{U}} 17 {{/U}} {{/U}}and the burning of {{U}} {{U}} 18 {{/U}} {{/U}}fuels have drastically {{U}} {{U}} 19 {{/U}} {{/U}}carbon dioxide in the atmosphere. So we enter into uncharted {{U}} {{U}} 20 {{/U}} {{/U}}now in terms of the amount of carbon dioxide.