Ever since the first global environmental summit in Rio de Janeiro more than 20 years ago, attempts to forge international agreements to combat climate change have been bedevilled by questions of equity between the developed and developing worlds.

While rich countries acknowledge an overwhelming responsibility for the historic growth in emissions, they reasonably argue that corrective action by them alone will not be enough to curb future increases at a global level, let alone start to drive them down.

The developing world meanwhile focuses on the prosperity the west’s careless use of carbon has allowed it to achieve. Apply too tight a curb on less prosperous states, these countries say, and the advanced economies will simply cement their developmental advantage. The result will be to trap billions of people at levels of income far below that which the inhabitants of America and Europe routinely enjoy.