The global appetite for energy is likely to swell far more rapidly than available supply in coming decades as oil production hits a plateau and emerging markets see rampant economic growth, Royal Dutch Shell has said.  In a report published today, the oil giant predicts that by 2050 world energy demand may have tripled compared with 2000 levels, based on historical patterns of development. However, energy supplies may grow by only 50 per cent in the same period.  Improvements in energy efficiency could curb demand by 20 per cent. But the world still needs to figure out how to bridge a looming gap between supply and demand that is equivalent to the global energy industry's entire output in the year 2000, Shell calculated. By the end of this decade the world will run into a plateau in oil production, a development that will put "upward pressure" on oil prices.  Jeremy Bentham, the vice-president for Business Environment at Shell, said: "The coming surge in energy demand reflects the surge in developing nations. China will be continuing through its industrialisation period over the next ten years, and India is probably ten years behind that.  "This will be followed by the likes of Indonesia, Vietnam, and so on. These successive waves of development will create a surge in underlying demand for energy. This is leading us to a vast zone of uncertainty."  The projections came in a report updating energy scenarios that Shell published in 2008. Since then the recession set global energy demand back by about two to three years, meaning that 2008 demand levels will be reached again only this year.  However the broader trend in energy markets is clear, the report said: the world faces rapid demand growth as emerging markets industrialise, coupled with increasing strains on traditional sources of energy. Oil production is likely to rise 16 per cent