At the time of the first major climate change conference, in Rio de Janeiro in 1992, China was one of the least developed nations. Its per capita income was below Haiti, Niger and Pakistan. The export sector was smaller than that of Sweden or Austria, and its airports saw fewer departures than Norway’s.

Its emissions were just 12% of the global total, and on a per-capita basis it wasn’t even in the top 50 emitters. As recently as 1985, China had generated less electricity than Canada, and produced less steel than West and East Germany.

With nations set to gather for the latest such meeting …