" Roughly 30 percent of the solar radiation directed toward the earth is reflected directly back into outer space. The remaining 70 percent is absorbed by earth and re-emitted outward as long-wave--or infra-red--radiation. While transparent to incoming solar radiation, certain gases--notably carbon dioxide, nitrous oxide, methane, and chlorofluorocarbons--absorb, or ""trap,"" this outgoing infra-red radiation near the earth's surface, producing...