1860 scientist john tyndall described a phenomenon we call the greenhouse gas effect. 1900 nobel prize winning swedish scientist svante arrhenius calculated that the doubling of co2 in the atmosphere would rise the earth"s average atmosphere. Greenhouse effect - natural mechanism that retains the heat emitted from the earth"s surface. Earth"s average temperature is at the moment around 14c. If the natural greenhouse effect did not exist, the average temperature would be around -19c. A range of different gases can act as greenhouse gases. Common denominator: they can absorb heat emitted from the earth and re-emit it. Discussion about the anthropogenic greenhouse effect is mostly concentrated on the so- called long-lived greenhouse gases. Most important ones are co2, methane, nitrous dioxide, cfc gases. In total they account for more than 97% of the direct effect of the long-lived gases on how much heat is retained in the atmosphere.