[en] The possibility of limiting the increase of the average earth atmospheric temperature to 2 Celsius degrees appears to belong to the past. Rich countries have succeeded in blocking or even reducing their emissions of greenhouse effect gases but they still rely heavily on fossil energies. As for developing countries their development is essentially based on fossil energies they use in a growing tendency. It is difficult to image how these trends could be reversed in a short time. In the article the carbon budget is defined as the cumulated quantity of carbon that will avoid exceeding a fixed value of temperature. For instance a 2 degrees increase of temperature correspond to a CO_2 concentration in the atmosphere of 450 ppm. In the case where nothing was done and that fossil energies were used until their exhaustion, the carbon budget would reach 657 ppm and the corresponding increase of temperature would be beyond 4 degrees. (A.C.)