The COP21 negotiators at the Paris 2015 convention enjoyed a rare moment of success. Unlike in Copenhagen six years before, the climate summit produced an agreement — and an ambitious one at that. The attending governments committed to keeping the temperature rise “well below 2° C” and “continuing efforts” not to exceed 1.5° C of warming. No one had imagined such a breakthrough.

There was a fly in the ointment, however, which French president François Hollande immediately pointed out: the parties had not agreed to introduce a carbon price, an element that had been at the center of capitalist climate strategy leading up to the summit. Six months before COP21, Hollande had said:

If we really want to send signals to the markets so that companies can make their decisions based on an economic optimum, which can be an ecological optimum, the question of the price of carbon is necessarily posed because it is the most tangible sign that can be addressed to all economic actors.