Allow us to explain this phenomenon systemically: The Earth’s surface is warmed by the sun’s short-wave radiation. This process in turn produces long-wave heat radiation, so-called infra-red rays, which are released back into the atmosphere and travel toward space. The greenhouse gases in the atmosphere absorb this radiation and release it in all directions, part of it going back to the Earth. This counter-radiation causes warming on the Earth’s surface and in the lowest layer of the atmosphere (the troposphere). As the concentration of greenhouse gases increases, so does the additional warming created by this greenhouse effect.
The natural greenhouse effect has made it possible for life to develop on Earth. According to current research, this effect produces a temperature difference of 33 °C. This means that without greenhouse gases, the median temperature on the Earth would be around -18 °C and life on Earth would have never developed as we know it today.
Only through the additional warmth generated by the natural greenhouse effect does the global average temperature reach +15 °C, making life possible. However, the natural balance between incoming and outgoing radiation is disturbed by human-caused greenhouse gases. Today, scientists measure 40% more CO2 than there was at the beginning of the Industrial Age. As a result, the Earth’s surface has warmed by 0.85 °C globally since the beginning of the 20th century.
This warming has initiated various feedback processes, which also have effects on the climate system. The absorption of more water vapour into the atmosphere as well as the decline of snow- and ice-covered surfaces lead to additional warming. There are, however, changes whose effect on the climate cannot yet be evaluated, such as changes to the cloud cover and the carbon cycle.
Source: PCC 2007 Glossar und Springer Gabler Verlag (Herausgeber), Gabler Wirtschaftslexikon, Bundesamt für Umwelt (BAFU)