Patrick Criqui, an expert in the prospects for energy and the environment, examines some of the recently proposed scenarios for energy needs and production and for global emissions of greenhouse gases. He thus points out that "between the pressure of demand, the upstream limits on resources and the downstream limits on emissions, devising long-term energy scenarios is an exercise in squaring the circle".
He summarizes here a range of scenarios including those of the IPCC (Intergovernmental Panel on Climate Change), those carried out as part of the study of Greenhouse Gas Reduction Pathways, and the Factor 4 scenarios (which aim to cut carbon emissions to a quarter of existing levels, notably in France). Among these scenarios, some are considered "policy free" (i.e. they do not set targets to aim for); others set targets expressed in precise figures for stabilizing or reducing greenhouse gas emissions. Patrick Criqui describes them in detail, showing what can be learned from each one, the controversies they stir up and their possible implications for public action, in particular. Lastly he discusses the policies that might be adopted in order to promote "virtuous" scenario outcomes (stabilizing emissions), with regard to technological innovations, economic incentives and in structural terms.