In June 2007, the Intergovernmental Panel on Climate Change of the United Nations published the three-part UN Climate Report, on which some 2,500 researchers from 124 countries had worked for years. It is based on around 40 computer simulations. For the first time it was agreed on a formulation according to which mankind is to blame for climate change (which, however, is still disputed in some places). The highly developed countries are responsible for heating up the atmosphere (global warming) and "exporting" the effects. The main causes are rapid population growth, increasing consumption of fossil fuels, deforestation and urbanisation.
The relentless combustion of fossil fuels such as petrol, oil or coal produces huge amounts of additional carbon dioxide, which causes the so-called greenhouse effect. It is contained in the earth's atmosphere as a trace gas with a volume fraction of about 0.038%. This proportion, which at first glance appears extremely low, is repeatedly mistakenly used by sceptics as an argument that the CO2 contribution of humans in the air is so small that it does not affect the climate. The basic assumption is that a small amount has only a small effect. But this is not the case. In many regions of the world, a decrease in the number of frost days and an increase in the number of days with extremely high temperatures has been observed in recent decades. This was particularly the case in central and northern Europe, the USA, Canada, China, Australia and New Zealand. In the central and northern latitudes, especially in the northern hemisphere, the frequency of heavy precipitation increased significantly in the second half of the 20th century. In contrast, some regions of Africa and Asia are experiencing increasingly frequent severe droughts, as well as desertification.