The latest report on global warming makes grim reading

IN 1996 the European Union became the first significant political body to suggest that the goal of preventing “dangerous anthropogenic interference in the climate”, to which the world had signed on at the Rio Earth summit of 1992, meant, in practical terms, keeping global warming below 2°C relative to the late 1800s. This two-degree limit had been an informal measure of the point where climate change gets serious since the 1970s. William Nordhaus, a pioneer of climate economics who this week shared the Nobel prize for his efforts (see ) seems to have been the first to use it as such. But between 1996 and the Copenhagen climate summit of 2009 it was transformed from one possible interpretation of the Rio goal to the target on which the world agreed.At the Paris climate summit of 2015, though, this changed. In light of both new evidence and new concerns, notably those of low lying countries that might not survive the amount of sea level rise two degrees would bring, the nations of the world agreed a new target: keeping warming “well below” 2°C above pre-industrial temperatures. Indeed, they urged themselves to “pursue efforts towards 1.5°C”.