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Why Uncertainty Matters - Discounting under Intertemporal Risk Aversion and Ambiguity

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  • Christian Traeger

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Abstract

Uncertainty has an almost negligible impact on project value in the economic standard model. I show that a comprehensive evaluation of uncertainty and uncertainty attitude changes this picture fundamentally. The analysis relies on the discount rate, which is the crucial determinant in balancing immediate costs against future benefits and the single most important determinant of optimal mitigation policies in the integrated assessment of climate change. The paper examines two shortcomings in the recent debate and the current models addressing climate change assessment. First, removing an implicit assumption of (intertemporal) risk neutrality reduces the growth effect in social discounting and significantly amplifies the importance of risk and correlation. Second, debate and models largely overlook the difference in attitude with respect to risk and with respect to non-risk uncertainty. The paper derives the resulting changes of the risk-free and the stochastic social discount rate and points out the importance of even thin tailed uncertainty for climate change evaluation. It discusses combinations of uncertainty and correlation that reduce the social discount rate to pure preference. In a theoretical contribution, the paper extends the smooth ambiguity model by providing a threefold disentanglement between, risk aversion, ambiguity aversion, and the propensity to smooth consumption over time.

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  • Christian Traeger, 2012. "Why Uncertainty Matters - Discounting under Intertemporal Risk Aversion and Ambiguity," CESifo Working Paper Series 3727, CESifo Group Munich.
  • Handle: RePEc:ces:ceswps:_3727
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    Cited by:

    1. Iverson , Terrence & Karp, Larry, 2017. "Carbon taxes and climate commitment with non-constant time preference," Department of Agricultural & Resource Economics, UC Berkeley, Working Paper Series qt3hw6s14v, Department of Agricultural & Resource Economics, UC Berkeley.
    2. Luciano I. Castro & Zhiwei Liu & Nicholas C. Yannelis, 2017. "Ambiguous implementation: the partition model," Economic Theory, Springer;Society for the Advancement of Economic Theory (SAET), vol. 63(1), pages 233-261, January.
    3. Svenja Hector(), "undated". "Accounting for Different Uncertainties: Implications for Climate Investments?," Working Papers ETH-RC-13-007, ETH Zurich, Chair of Systems Design.
    4. Yongyang Cai & Kenneth L. Judd & Thomas S. Lontzek, 2013. "The Social Cost of Stochastic and Irreversible Climate Change," NBER Working Papers 18704, National Bureau of Economic Research, Inc.
    5. Fleurbaey, Marc & Zuber, Stéphane, 2015. "Discounting, beyond utilitarianism," Economics - The Open-Access, Open-Assessment E-Journal, Kiel Institute for the World Economy (IfW), vol. 9, pages 1-52.
    6. van den Bijgaart, Inge & Gerlagh, Reyer & Liski, Matti, 2016. "A simple formula for the social cost of carbon," Journal of Environmental Economics and Management, Elsevier, vol. 77(C), pages 75-94.
    7. Crost, Benjamin & Traeger, Christian P., 2013. "Optimal climate policy: Uncertainty versus Monte Carlo," Economics Letters, Elsevier, vol. 120(3), pages 552-558.
    8. Christian Traeger, 2014. "A 4-Stated DICE: Quantitatively Addressing Uncertainty Effects in Climate Change," Environmental & Resource Economics, Springer;European Association of Environmental and Resource Economists, vol. 59(1), pages 1-37, September.
    9. Simon Quemin, 2016. "Intertemporal abatement decisions under ambiguity aversion in a cap and trade," Working Papers 1604, Chaire Economie du climat.
    10. Hector, Svenja, 2015. "Extending the Ramsey Equation further: Discounting under Mutually Utility Independent and Recursive Preferences," Annual Conference 2015 (Muenster): Economic Development - Theory and Policy 113061, Verein für Socialpolitik / German Economic Association.
    11. Hiroaki Sakamoto & Ken-Ichi Akao, "undated". "A theory of disasters and long-run growth," Discussion papers e-17-014, Graduate School of Economics , Kyoto University.
    12. Svenja Hector, 2013. "Accounting for Different Uncertainties: Implications for Climate Investments?," Working Papers 2013.107, Fondazione Eni Enrico Mattei.
    13. Lemoine, Derek & Traeger, Christian P., 2016. "Ambiguous tipping points," Journal of Economic Behavior & Organization, Elsevier, vol. 132(PB), pages 5-18.
    14. van den Bijgaart, Inge, 2016. "Essays in environmental economics and policy," Other publications TiSEM 298bee2a-cb08-4173-9fe1-8, Tilburg University, School of Economics and Management.
    15. Howard, Peter H. & Derek, Sylvan, 2016. "The Wisdom of the Economic Crowd: Calibrating Integrated Assessment Models Using Consensus," 2016 Annual Meeting, July 31-August 2, 2016, Boston, Massachusetts 235639, Agricultural and Applied Economics Association.
    16. Chambers, Robert G. & Melkonyan, Tigran, 2017. "Ambiguity, reasoned determination, and climate-change policy," Journal of Environmental Economics and Management, Elsevier, vol. 81(C), pages 74-92.
    17. Freeman, Mark C. & Groom, Ben, 2016. "How certain are we about the certainty-equivalent long term social discount rate?," Journal of Environmental Economics and Management, Elsevier, vol. 79(C), pages 152-168.
    18. Iverson, Terrence, 2013. "Minimax regret discounting," Journal of Environmental Economics and Management, Elsevier, vol. 66(3), pages 598-608.
    19. Larry S. Karp, 2012. "Provision of a Public Good with Altruistic Overlapping Generations and Many Tribes," CESifo Working Paper Series 3895, CESifo Group Munich.
    20. Jensen, Svenn & Traeger, Christian P., 2014. "Optimal climate change mitigation under long-term growth uncertainty: Stochastic integrated assessment and analytic findings," European Economic Review, Elsevier, vol. 69(C), pages 104-125.

    More about this item

    Keywords

    ambiguity; climate change; cost benefit analysis; discounting; intertemporal substitutability; risk aversion; uncertainty;

    JEL classification:

    • D61 - Microeconomics - - Welfare Economics - - - Allocative Efficiency; Cost-Benefit Analysis
    • D81 - Microeconomics - - Information, Knowledge, and Uncertainty - - - Criteria for Decision-Making under Risk and Uncertainty
    • D90 - Microeconomics - - Micro-Based Behavioral Economics - - - General
    • H43 - Public Economics - - Publicly Provided Goods - - - Project Evaluation; Social Discount Rate
    • Q00 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - General - - - General
    • Q54 - Agricultural and Natural Resource Economics; Environmental and Ecological Economics - - Environmental Economics - - - Climate; Natural Disasters and their Management; Global Warming

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