Optimal Timing of CCS Policies under Decreasing Returns to Scale

Carbon capture and sequestration (CCS) can help to mitigate the climate change transition. Usually, in models where the atmospheric carbon stock is constrained by an institutional stabilization cap and under constant average CCS cost, the use of CCS must be delayed up to the time at which the constraint begins to be e@ective. In this paper, we show that, when abatement activity are submitted to decreasing returns to scale, abatement must start earlier, before the climate constraint becomes to bind, but they must also be stopped strictly before the climate constraints ceases to be active. Depending on the solar energy costs, either there is a return toward dirty energy or either a progressive rise of solar energy at the expense of abatement activities.