文档介绍：Global Warming There is one of the most sensitive global climate issues for years, which is global warming. In general, we know that the origin of global warming is the emi ssion of carbon dioxide . It was verified that the relationship between carbon dioxide and temperature: when there is more carbon dioxide the temperature gets warmer. This topic should be discussed under current situation to advocate people concerning with this severe environmental issue. Meanwhile, people should consider how to reduce the emission of carbon dioxide and take some actions to stop global warming. What is global warming? What caused global warming? What are the negative effects caused by global warming? What can we do to save the earth? Are there any positive effects? In the next paragraphs, I will explain these questions in details. What is global warming? Global warming is the increase in the average temperature of Earth 's near-surface air and oceans since the mid- 20th century and its projected continuation ( Brown 22). According to the 2007 Fourth Assessment Report by the Intergovernmental Panel on Climate Change , global surface temperature increased ± °C ( ± °F) during the 20th century ( Keppler ). In nearly 100 years, the average global temperature goes through four fluctuations : cold, warm, cold again, and warm again. After 1980s, the temperature was ascending obvio