This article considers the usefulness of low-carbon scenarios in public decision-making. They may be useful as a product-oriented trajectory. The scenarios on the agenda of the 2013 Energy Debate in France belong to this category. But a scenario may also be process-oriented, in the sense that its scripting process helps build consensus and a minimum level of agreement. We have scripted scenarios using a codevelopment method, involving about 40 stakeholders from the private and public sectors, and from the state: NGOs, consumer groups, trade unions, banks and local authorities. They selected policies they considered acceptable for achieving 75% greenhouse gases emission reductions in 2050. These policies were then integrated in the Imaclim-R-France technico-economic simulation model, as part of a high or moderate acceptability scenario. In the first case emissions were cut by between 58% and 72% by 2050; in the second case by between 68% and 81%, depending on the energy price assumptions. All these measures benefited jobs and economic growth, swiftly and durably cutting household spending on energy services. This offers a solid basis for gaining acceptability for low carbon trajectories; the process constitutes also a framework for consolidating collective learning centering on the acceptability of climate policies.