The development of the global climate shows that the Earth's average surface temperature, though fluctuating, has been rising every year since the beginning of the 20th century. The trend is that the temperature increase is higher in winter than in summer.

Various methods have proved that the causes of the increase in the global average surface temperature are not merely natural but widely the consequence of man-made changes of the atmosphere's composition. Since the beginning of the Industrial Age some 130 years ago, the concentration of greenhouse gases in the atmosphere has increased dramatically. Even new greenhouse gases like chlorofluorocarbons (CFCs) have been developed. Due to the relatively long residence times of greenhouse gases in the atmosphere (of partly more than 100 years), they are accumulated in the atmosphere.

The main causes of this development are the combustion of fossil fuels and the burning of tropical rainforest. If the man-made greenhouse effect is further increased, the warming of the Earth will continue. The 20th century was the warmest century in at least 600 years and the one with the fastest changes. The impacts for nature and every aspect of society are diverse and not yet completely foreseeable (e.g. rising sea levels, changing patterns of precipitation, increase of extreme weather events).