1. World energy use
The rapidly growing world energy use has already raised concerns over supply difficulties, exhaustion of energy resources and heavy environmental impacts (ozone layer depletion, global warming, climate change, etc.). The International Energy Agency has gathered frightening data on energy consumption trends. During the last two decades (1984–2004) primary energy has grown by 49% and CO2 emissions by 43%, with an average annual increase of 2% and 1.8% respectively (Fig. 1).