The Earth is surrounded by windows. We call these windows the atmosphere, a layer of air many miles up in the sky. As the sun shines on the Earth, the atmosphere lets the heat reach the ground, then prevents some of it from escaping back into space. That's all fine. In fact, we need the atmosphere. Without it, the Earth would be as cold and lifeless as the surface of the moon. The problem is that our atmosphere is changing. Some of our favorite activities create gases that pollute the atmosphere. As those gases build up, the atmosphere keeps in too much heat.
What are Greenhouse Gases?
