Is there any significant likelihood that policy action will eliminate the risk of climate disaster? At present, the answer is no.

This is so, even though leaders of the group of seven leading high-income countries say they support cutting emissions by 40 to 70 per cent by 2050. It is so, even though a major global conference in Paris at the end of the year aims to reach a universal and legally binding agreement, enabling “us to combat climate change effectively” and boost the transition towards “resilient, low-carbon societies and economies”.

Why should we be sceptical? The answer is that we have heard similar commitments for nearly a quarter of a century; and yet we have only seen rising flows of emissions and stocks of greenhouse gases in the atmosphere. Even if governments met current commitments (itself unlikely), atmospheric concentrations of carbon dioxide would rise towards 700 parts per million by the end of the century, as against 280 ppm before the industrial revolution and some 400 ppm now. With 700 ppm, the median increase in expected global temperature is 3.5C. Keeping emissions on the path needed to limit the median expected increase to the recommended 2C — and then delivering — would require a revolution. (See chart)