"Factories of death" is how James Hansen, a crusading American scientist, describes power stations that burn coal. Coal is the dirtiest of fossil fuels, producing twice the carbon dioxide that natural gas does when it is burned. That makes it a big cause of global warming.
But some of the world's biggest economies rely on coal. It provides almost 50 percent of America's and Germany's power, 70 percent of India's and 80 percent of China's. Digging up coal provides a livelihood for millions of people. And secure domestic sources of energy are particularly prized at a time when prices are volatile and many of the big oil and gas exporters are becoming worryingly nationalistic. It is hard to see how governments can turn their backs on such a cheap and reliable fuel.
There does, however, seem to be a way of reconciling coal and climate. It is called carbon capture and storage (CCS), or carbon sequestration, and entails hoovering up carbon dioxide from the smokestacks of power plants and other big industrial facilities and storing it safely underground, where it will have no effect on the atmosphere. The technologies for this are already widely used in the oil and chemical industries, and saltwater aquifers and depleted oilfields offer plenty of promising storage space. Politicians are pinning their hopes on clean coal: Angela Merkel and Barack Obama, among others, are keen on the idea.