Les impacts économiques du changement climatique : enjeux de modélisation

Large differences remain between various assessments of the economic impacts of climate change and of the cost of mitigation policies. These are partly due to a number of questionable assumptions in energy-economic modeling, originating in a value system one should be aware of. This study sets up a frame of reference to analyze the impact of modeling choices on the results. Energy-economic models are analyzed, with four examples: ENV-Linkages, GEMINI-E3, IMACLIM-R and POLES. Top-Down models do not catch enough technical progress potentials, whereas Bottom-Up models do not model satisfactorily the feedback effects of the energy sector on the rest of the economy. Recursive dynamic models do not take enough into account the agents’ expectations and cannot build normative scenarios. On the contrary, some hybrid models and all the intertemporal optimization models include an endogenization mechanism which confuses the results. We then analyze the consequences of theoretical differences between models on a practical case: the assessment of the economic value of carbone by GEMINI-E3, IMACLIM-R and POLES. The Stern Review is analyzed in the broader framework of economic growth-environment modelization. The differences in results with other “cost-benefit” models are due to incomplete knowledge of future damages, the choice of an actualization rate and the assessment of non-market damages.