During the year to date, the share price of Peabody Energy, the world's largest private coal producer, has risen more than sixfold, making it one of the best investments among energy companies or indeed, any industry category. This was largely because the price of coal, the most unloved of energy sources, has been on a tear, more than tripling since the start of this year.

There is a connection between these developments and what has been happening lately in China and India, which together account for about two-thirds of the global demand for coal. Over recent days, there have been rolling blackouts in Beijing, Shanghai and many cities in the rust belt of China's north-eastern provinces because of crippling power shortages.