Combustion of fossil fuels increases permanently the carbon content of the fast carbon cycle consisting of atmosphere,land and surface ocean.The carbon residence times in these reservoirs are relatively low in the order of some years.Hower,the carbon residence time in the whole fast cycle is in the order of 2,000 years.This means the final storage problem of fossil energy use is in the same order as that of nuclear energy use. There are two other main driving forces for a continuous decarbonisation of the world energy system.The first one is the shortening of raw materials,an the second one is the greenhous gas effect of carbon dioxide with the risk of climate change. Based on the "molecular fingerprints"of various fossil fuels a new quantity.the "energetic carbon efficiency"can be derived.This quantity favours methane(natural gas)more than any other fossil fuel.E.g.,methane is two times more efficient than lignite or hard coaL Therefore,the future role of this energy carrier will be discussed more in detail. Carbon capture and storage(CCS)is not a convincing concept and therefore it cannot be considered as a responsible excuse for new coal fired power stations.A reasonable way out may be the carbon moratorium.This means a thermal splitting of methane into carbon and hydrogen.Only the hydrogen is used as a fuel whereas the carbon is deposited in the earth,because storage of carbon is much safer than storage of carbon dioxide. Very often biofuels are considered as a sustainable option.Critical arguments are presented against the meander of biofuels. Negative climate implications and very low efficiencies are serious arguments against these teehnolgies.Even the fashionable new hope for bioenergy from algea farms has no rational fundament. A long-time sustainable energy system requires not only low carbon but zero carbon technologies.This means solar energy in all kinds of its appearance(water power,wind,solar heat and photovoltaics).However these kinds of energy require new energy storage technologies.Various storage technologies will be discussed with a special focus on electrochemical batteries and electromobility. All of these new energy technologies are not able to remove any carbon from the fast carbon cycle.Therefore,some prominent concepts of climate engineering will be introduced.