Scientists have shown that the Earth's average temperature has risen slightly in the last few decades. We know that the climate really changes because of global warming. And this can have a huge effect on life on the Earth.

　　Scientists believe the Earth's average temperature has risen slightly in the last few decades. 近几十年地球的平均气温正在缓慢提升。

　　For about the last 10,000 years, the average temperature of the Earth has been about 15°Celsius（摄氏度） (59°Farenheit华氏度). During this time, the Earth's average temperature has not changed by more than 1°C (1.8°F). Scientists can now document（证明） that the average temperature of the Earth has risen about 0.5°C (0.8°F) since 1850. Additionally, the 1990's was the warmest decade ever recorded. Scientists predict that the Earth will warm 1.0° to 3.5°C (1.8° to 6.3°F) in the next 100 years. This appears to be the most rapid and greatest warming of Earth's temperature than has ever occurred. 一万年前，地球的平均气温是15摄氏度。到了1850年，平均气温只上涨了0.5摄氏度。然而，科学家预测在未来的百年内，平均气温就要上涨1-3.5摄氏度。 变暖速度之快之巨在之前绝无仅有。

　　What is causing Global Warming? 什么因素导致了全球变暖？

　　Many factors contribute to the Earth's temperature, including the shape of the Earth's revolution around the Sun, the Earth's tilt（倾斜） on its axis（轴）, the way the Earth wobbles（摇晃，摆动） on its axis, solar activity such as sun spots（太阳黑子）, and the chemical composition of Earth's atmosphere. Scientists believe that human activities are affecting the chemical composition of Earth's atmosphere. 导致全球变暖的原因很多，包括地球公转自转的角度变化，太阳黑子的频繁活动，大气的物质构成发生变化等等。而后者的变化正是人为因素造成的。

　　How are human activities affecting Global Warming? 为什么人类的活动会引发全球变暖？

　　Earth's atmosphere is 78 percent nitrogen（氮） and 21 percent oxygen. Less than one percent of the atmosphere is carbon dioxide, water vapor, methane, nitrogen oxides, and ozone, which are known as greenhouse gases. Greenhouse gases act like the panes（长方块） of glass in a greenhouse. They keep some of Earth's heat from escaping to space. Until about 100 years ago, the concentration （密度，浓度）of greenhouse gases in Earth's atmosphere was stable. Scientists believe that human activities are changing the concentration of greenhouse gases in Earth's atmosphere. Specifically, they are concerned about how much carbon dioxide, methane, and nitrogen oxides are being added to the atmosphere as a result of human activities. Just like adding an extra blanket to your bed will keep you warmer, more greenhouse gases will keep the planet warmer. 大气主要由78%的氮气和21%的氧气构成，剩下的1%被称作温室气体，由二氧化碳、水蒸汽、甲烷、臭氧等组成。温室气体阻止地球热量的散失。100年前，温室气体在大气中的含量还很稳定，但如今，人类的活动排放出大量的二氧化碳、甲烷、氧化亚氮，致使温室气体在大气中的浓度提升。过多的温室气体就像睡觉添加的被子一样，会让人们觉得更暖和，会导致全球气候变暖。liuxuepaper.com