【專八mini系列】溫室效應(yīng)（1/7）

Good morning. Today's lecture is about the Greenhouse Effect. The “greenhouse effect" often gets a bad rap because of its association with global warming, but the truth is we couldn't live without it. First, I'd like to ask you what causes the greenhouse effect. Life on earth depends on energy from the sun. About 30% of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planet's surface and is reflected upward again as a type of slow-moving energy called infrared radiation. As it rises, infrared radiation is absorbed by greenhouse gases such as water vapor, carbon dioxide, ozone and methane, which slows its escape from the atmosphere. Although greenhouse gases make up only about 1% of the Earth's atmosphere, they regulate our climate by trapping heat and holding it in a kind of warm air blanket that surrounds the planet. This phenomenon is what scientists call the “greenhouse effect."