2. 450 ppm: the predetermined framework for economists' thinking

In developing their tools, economists can reason in two ways.

The first, familiar to us in the land of Descartes, is based on the application of a rationality from the general to the particular, taking as its first assumption the need for man to "maximize net well-being", evaluated in our case as the difference between the economic benefits linked to (industries that generate) GHG emissions, from which we subtract the cost of the environmental damage caused by the concentration of GHGs in the atmosphere. We thus arrive at an optimum, for which the level of emissions is determined by a balance between marginal benefit and marginal damage. A clear example of this approach was provided by the Stern Report in 2006, which made a decisive contribution.