Last year was the second warmest in Britain since records began and CO₂ levels have gone up by almost a fifth in the past five decades; but, as every well-briefed journalist knows, global warming is a myth put out by charlatans, so there can be no cause for concern. No, in 2012 we should worry instead about carbon’s neighbour in the periodic table of the elements. The triumph – or disaster – of nitrogen began exactly a century ago, when in 1912 a pilot plant in North Germany began to pump out the raw material of a new agricultural fertiliser.