IPCC claims that Global Warming is caused more or less exclusively by anthropogenic emissions of CO2. Therefore, only a total stop of these emissions could avoid a disaster. In IPCC’s reasoning, two concepts are central: The “constant airborne fraction”, according to which about 50 % of all anthropogenic emissions remain in the atmosphere, whatever the emissions and whatever the concentration, and the “fixed carbon budget”, which is the maximum amount humans may emit, when Global Warming should stay below a given limit, independent of the temporal distribution of the emissions. In this article, it is shown that three prerequisites must be fulfilled for these two central concepts to be viable: All natural sources of CO2 must have remained constant, the short-term partners of the atmosphere must store the same amount of CO2 as the atmosphere itself, and the atmosphere together with its short-term partners must be a closed system. And it is shown with high confidence that, according to the rules of physics, all three are not fulfilled. If this were confirmed, it would have a serious impact on the entire climate debate. A careful review seems to be needed urgently.