Moore's law has worked up to around these days (it looks to be slowing down). It states that the speed of the processor doubles about every two years (more precisely it states number of transistors on an integrated circuit doubles but it's about the same).
Conversely it also means power requirements go down at around the same pace.
Today, humanity fabricates 1,000 times more transistors annually than the entire world grows grains of wheat and rice combined.
A single iPhone at 1980 energy-efficiency would require as much power as a Manhattan office building.