Talking about scenarios, The calumatic scenarios raises the question of what is a scenario. A scenario is quite simply the representation of a possible future for prospective purposes. Therefore, this future story must be an exploration, it must be plausible, that it must not be incompatible with the laws of physics, it should not move away too much from the economic theory or if so, in an explicit way. A scenario should not be likely. We are not even trying to estimate the likelihood of the scenario ever coming true. It's not there to represent the complexity of the surrounding world. Therefore, the scenario may be simplistic or idealized. Finally, a scenario may be utopic or unacceptable. Climate scenarios are not there to become a rule in a given type of future. Therefore, we look at not one, but several scenarios at the same time. There are two approaches in a way a climate scenario is prepared. The first one is a sequential approach. We're talking about a socio-economic scenario which may then be translated in Greenhouse Effect gas emission scenario. Then, because we have knowledge on the biogeochemical cycles, we can translate this in a scenario on concentration of Greenhouse Effect gases. We can assess the ATAV-forcing associated with the concentration tracks and finally predict a climatic projection. Conversely, there is the other approach, which is called the reverse approach, starting from a scenario on Greenhouse Effect concentration, a radiative forcing scenario, from where we can assess, estimate, a climatic scenario, based on which we can, a posteriori, reconstruct socio-economic scenarios which we compatible with the Greenhouse Effect gas scenario. The radiative forcing scenario could therefore correspond to several scenarios. This is the approach chosen for the fifth IPCC assessment scenario or report. Because first, we can move away from the political debate and two, because it allows to take into consideration scenarios with policies that aim at reducing Greenhouse Effect gases emissions. Here we have RCPC scenarios, representative concentration, pathways used for the fifth IPCC report. Radiative forcing varies between two values, providing the name of the RCPC scenarios, 2.6 and 4.5, extreme scenarios, sorry, 8.5, extreme scenarios for radiative forcing. These scenarios imply carbon dioxide emissions shown on the left for the RCPC 2.6 scenario emissions should reach a maximum ceiling value very quickly and decrease down to the year 2018, whereas for the RCPC scenario 8.5 emissions will continue increasing until they reach. 27 CO2 guagatons in 2100, three times more than the current emissions. These scenarios were then prolonged beyond the 21st century in a stylized manner and we have dotted lines on the two graphics representing this. Carbon dioxide is not the only Greenhouse Effect gas that we need to make predictions on. We are looking at scenarios for the other Greenhouse Effect gases, especially methane, CH4 and nitrous oxide and 2O, shown on this picture. The Green, the grey areas try to surround all of the possible future scenarios within without emission mitigation policies being implemented. Greenhouse Effect gases are not the only factors influencing the climate. There are also short-life cycle pollutants which have an impact on the climate such as sulfur dioxide, responsible for a negative radiative forcing because it forms a sulfur aerosol and cools down the climate or nitrogen oxide which combined with volatile compounds, organic compounds, forms ozone and other Greenhouse Effect gas. These short-life cycle pollutants also have an impact on air quality. Generally speaking, one may consider that their emissions or their concentrations will decrease during the 21st century at a rate that will depend on the various types of assumptions made on economic growth and the convergence between developing countries and industrialized countries. There are also different parameters in order to characterize socioeconomic scenarios such as primary energy consumption, the energy mix and two more parameters, shown here, the emission factor expressed in kilograms of carbon released in the atmosphere by unit of used energy. This factor decreases rather slowly for the RCP 6 and 8.5 scenarios which are very strong in radiative forcing but decreases much faster for scenarios 4.5 and 2.6 due to the introduction of renewable energies and also due to the implementation of the carbon uptake and storage. Just at the exit of the chimneys for further production power plants. Here we have the energy intensity on the right hand side. The quantity of energy needed to produce one dollar worth of PIB, wealth in other terms. This factor decreases in all scenarios but it depends on the type of economy towards which the scenario is oriented. In conclusion, a climatic scenario requires good knowledge of emissions or greenhouse effect gas concentrations, good knowledge of emissions and pollutant concentrations when these pollutants are short life cycle pollutants. The way land is used on the continent because this is a limiting condition and finally if we want to translate the climatic projections with the impact projections for both the ecosystem and human society. We need to combine the projections with underlying socioeconomic data which can be found in scenarios such as population, degree of urbanization, society structure, agriculture, industry etc. There are still an answer to questions, open questions on climatic scenarios. One may wonder for instance what about extreme scenarios 2.6 and 8.5? Are they plausible? And we need to analyze parameters and assumptions with socioeconomic models such as the rate at which emissions are going to be decreased. Can we reach a decrease of several percent per year? Or yield? Growth for agriculture and extraction of fossil fuels bearing in mind that socioeconomic scenarios are not independent from climatic scenarios because there is ritual action or possible ritual action between climate evolution and climatic policies. One may expect that if sensitivity of climate to a greenhouse effect is high that policies will become more ambitious in the 21st century. Other parameters have to be taken into consideration but they are uncertain or sometimes not taken into consideration. For instance the fact that there may be massive emission of methane hydrates contained in marine sediments or massive emissions of CO2 and CH4 following thought of perjelisol in Siberian Canada and on the socioeconomic side we can envisage technological divides or the use of geoengineering climate techniques. Therefore these scenarios must be considered as one option for the future.