Consensus exists that further environmental pollution and climate change could be prevented if energy systems' emissions are significantly reduced. But energy will remain one of the most active driving forces of social and economic progress over the whole 21st century. This predetermines the necessity and expediency for long-term energy studies. Global energy systems recently have started the transition path from systems based on fossil fuels, with limited and exhaustible resources, to systems using inexhaustible or renewable energy resources (fission and fusion, solar, wind, biomass, geothermal, etc.). It is difficult to foresee exactly how long this transition period will last, because the rates of transition will depend on many factors — of which the most important will be energy costs at the end-user and the systems' impacts on humans, biosphere, and natural environment. Two global energy scenarios (Dynamic-as-Usual and Enhanced Energy Efficiency and Conservation, with several options for each of the scenarios) until the middle of the next century are discussed in the paper. According to energy projections, energy demand in developed countries is likely to stay at the current level over the whole time period or may even slightly decline (it is quite possible that in some countries with very high per capita energy demand, the reduction of primary energy consumption will start even in the near future). The major part of the energy demand growth worldwide will be justified by the needs of developing countries to improve their economic and social position. It is expected that primary energy demand in developing countries will increase by a factor of 3–5 compared to today's level. The world primary energy mix will very much depend on development strategies applied over the next 50–60 years. If a strategy for massive prevention of global warming is to be required, the share of fossil fuels in primary energy consumption must be remarkably reduced (even down to 25% in case of a 60% CO 2 emission reduction until the middle of the next century as stated by IPCC). Electricity keeps its position as a most universal energy carrier in all sectors of end-use, including transportation. Environmental protection goals can be achieved with the most effective and less expensive ways through applying electric technologies. Therefore, a strong growth rate for electricity generation is projected in both regions — developed and developing countries. Even if radical steps are taken to prevent the impact of energy systems on global climate, the CO 2 accumulation in the atmosphere will not be stopped. At the best, we can speak only of postponing the doubling of carbon concentration in the atmosphere for a couple of decades in the longer future. Parallel efforts within other spheres of the human activity are required: first of all, to stop deforestation of tropical forests, enhance reforestation, and reduce emissions of other greenhouse gases which in total contribute about 50% to global warming. The transition to an accelerated CO 2 reduction policy will require about 4–5% of the world GNP spent on investments within energy systems, which is not significantly higher than today. However, the structure of investments must be drastically changed from energy production to energy conservation and savings. Large concerns exist in finding capital to provide these investments in developing countries because it will be hardly possible for them to accomplish energy/climate programs without strong assistance from the developed world. It would be naive to think that a global energy and climate change policy could be introduced without massive obligatory measures at the national and global levels. These measures should include policy actions, marketing guidelines, educational programs, financial mechanisms, and technology transfer. The realization of such a policy will require the creation of new institutional frameworks, with concerted efforts of all players on the international and national energy markets. However, there are still many unsettled questions that remain in global warming and in looking for effective response strategies.