Energy is the driving force behind the planet's systems and human societies.
All living things need energy to survive - plants grow with energy from the sun and this in turn provides energy, in the form of food, to other living things. With death and decay, energy is released for other uses, nevertheless staying within the Earth's systems. Until a few hundred years ago, the energy cycles on Earth were not greatly disrupted by human development. Industrial activities have changed the delicate balance. Human aspirations have demanded huge quantities of energy in manufacture, agriculture, commerce, travel and domestic life.