Sometimes a quite simple new discovery or technological breakthrough changes everything, making nonsense of yesterday's apparently safe assumptions and expert projections.

The classic and often quoted example used to be the 19th-century forecast that all London' streets would inevitably become blocked with horse manure due to soaring growth in horse-drawn traffic. Then along came the motorcar, and that was the end of that scare.

A similar discontinuity could be about to hit the world of energy-supply forecasting. For some years now energy experts have been warning about the growing demand for natural gas to replace coal, especially for power generation.