In June 2007, the United Nations Intergovernmental Panel on Climate Change 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, agreement was reached on a formulation according to which humans are to blame for climate change (although this is still disputed in some places to this day). The highly developed countries are responsible for heating 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 burning of fossil fuels such as petrol, oil and coal produces huge amounts of additional carbon dioxide, which causes the so-called greenhouse effect. It is contained as a trace gas with a volume share of about 0.038% in the earth's atmosphere. This, at first sight, extremely small proportion is repeatedly and wrongly used by sceptics as an argument that the human contribution to CO2 in the air is so small that it does not influence 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 frosty days and an increase in the number of days with extremely high temperatures have been observed in recent decades. This has been particularly the case in central and northern Europe, the USA, Canada, China, Australia and New Zealand. In the middle 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.