The greenhouse effect occurs when radiation from the sun passes through the atmosphere and hits the surface of the Earth, which then absorbs it, heats up and emits infrared radiation. Greenhouse gases in the atmosphere absorb most of this infrared radiation and then radiate in the infrared range, which is emitted upward and downward, with part of it absorbed by other atmospheric gases further raising their temperature, part of it escaping to space, and another part reŸected downward toward the Earth’s surface (Figure 1.1). The surface and lower atmosphere are warmed by the part of the energy that is radiated downward, making our life on Earth possible. Without the greenhouse effect, the Earth’s temperature would be about 60ºF lower than it is now and too cold for life to exist here.