In today's global energy mix with a share of 80% fossil energy, the growth of the world population and energy demand will lead to a conflict between stable ecosystems and global welfare. The inspection of social indexes of welfare and happiness leads to the following energy plan: high-income countries with a current annual energy demand of up to 8 tonnes of oil equivalent per capita (toe pc) have to reduce their demand to 2 toe pc, which should be sufficient without cutback in welfare. Vice versa, low-income countries increase their demand until 2 toe pc are reached. Compared to today this scenario (2 toe pc, 9 billion people by 2050) leads to an increase of the ecological footprint from today 1.3 to 2 planet Earths in today's technologies. The only solution to provide 2 toe pc without damaging the biosphere is a reduction of the CO2 footprint with a current share of 50%. A complete shift from fossil fuels to renewables would half the ecological footprint as needed for the desired footprint of one planet Earth. To reach this goal, one or more forms of solar power and/or nuclear power are needed, as the potential of non-solar renewables is too small. (C) 2010 Elsevier Ltd. All rights reserved.