The importance of coal in America's energy mix has indeed tumbled since 1997, from almost half of electricity generation to just 36.7% in February, according to America's Energy Information Administration (see chart). This has come about mostly because of an increase in the use of natural gas (from 21.6% to 29.4% over the same period) rather than renewable energy (from 8.3% to 12.1%).



However, the numbers may not be welcome among all environmentalists, some of whom tend to loathe shale gas because of the “fracking” process through which it is released from rock formations. Some greens claim that fracking contaminates the air and groundwater and can even cause earthquakes (although there is no evidence linking fracking to increased seismic activity, according to the US Geological Survey).



Whatever the dangers of fracking, American manufacturers are enjoying cheaper energy. Thanks to shale gas, natural-gas prices in America are as low as they have been this decade (although talk of America achieving the holy grail of energy independence any time soon seems a bit premature).



Europe, on the other hand, has had no such luck. On the continent the price of natural gas has risen back to near pre-recession highs. What is more, the price of emitting carbon under the European Union's Emissions Trading Scheme has dropped below €7 ($9) per tonne, less than half its peak in mid-2011.



As a result, the economics of energy in Europe have moved in coal's favour (see charts below). In France and Germany, for instance, the “clean spark spread”—the theoretical gross margins from selling electricity after buying the gas required to produce it and the right to emit the carbon dioxide—is negative, meaning that the gas needed to fuel a power planet costs more than the electricity produced. In Britain this spread remains (just) positive, but operators must still cover the costs of building, running and maintaining power plants.