Over the period 1990 to 2006, energy productivity increased at an average rate of 1.3 percent, but from 2000 to 2006, productivity grew 1.5 percent per year.

China was the principal exception, with its improvement in energy productivity falling to 1 percent per annum in 2000-2006 from 7.5 percent per annum in 1990-2000, as its economic growth soared to double-digit levels.

The development of more efficient technologies over time generally allows countries to use less energy to perform the same tasks. However, total energy use still tends to rise as increased wealth prompts greater overall consumption.

Governments need to adopt a range of measures to reduce energy waste and unnecessary CO2 production, the report said, including tax breaks for energy-saving technology, rises in energy prices and tougher regulations for cars and houses.

Few countries around the world have so far managed to generate a material portion of their energy needs from sustainable or "green" sources, leading to increased hydrocarbon use and higher CO2 emissions.

Many analysts believe that until cleaner technologies are developed and adopted, energy efficiency is the easiest way for the world to significantly curb CO2 emissions.