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Ladies and Gentlemen. Good afternoon! I’m very glad to stand here and give you a short speech. My topic today is global warming.At present, humans face a serious challenge. That is global warming. Increasing global temperatures are causing a broad range of changes in the world. Sea levels are rising due to the melting of land ice.As you can see, global warming is a very serious threat to our lives，so it is important to learn more about it.Generally,global Warming is caused by two things. One is man-made, another is natural causes.One natural cause is the release of methane gas from arctic tundra and wetlands. Another natural cause is that the earth goes through a cycle of climate change. This climate change usually lasts about 40,000 years.Man-made causes probably do the most damage. There are many man-made causes. Pollution is one of the biggest man-made problems. Pollution comes in many forms. Burning fossil fuels is one thing that causes pollution. Fossil fuels ,such as coal or oil. When they are burned, they give off a green house gas called carbon dioxide.Another major man-made cause of global warming is population increase. More people mean more food, and more methods of transportation, right? That means more methane because there will be more burning of fossil fuels, and more agriculture. Another source of methane is manure. Animals like cows are raised as a source of food which means more manure and methane. Another problem with the increasing population is transportation. More people mean more cars, and more cars mean more pollution. Also, many people have more than one car.In the past few years, many workers have noted that the combined effect on climate of increases in the concentrations of a large number of exraust could rival or even exceed that of the increasing concentration of carbon dioxide. These exraust, principally methane and nitrous oxide, are present at concentrations that are two to six orders of magnitude lower than that of carbon dioxide, but are important because, per molecule, they absorb infrared radiation much stronger than carbon dioxide.Studies have shown that human activity of this century has increased the concentrations of atmospheric exraust, which in turn has elevated global surface temperatures by blocking the escape of thermal infrared radiation. Natural climate variations are masking this temperature increase, but further additions of exraust during the next 65 years could double or even quadruple the present effects, causing the global average temperature to rise by at least 1 °C and possibly by more than 5 °C. If the rise continues into the twenty-second century, the global average temperature may reach higher values than have occurred in the past 10 million years.However, assessment of ongoing and future climate change requires long-term global monitoring of aerosol properties.So there is a need and opportunity for global cooperation in technology development. Only by doing so that we can better live in this planet.Thank you!。
