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Why Uncertainty Matters - Discounting under Intertemporal Risk Aversion and Ambiguity

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  • Christian Traeger

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.

Suggested Citation

  • Christian Traeger, 2012. "Why Uncertainty Matters - Discounting under Intertemporal Risk Aversion and Ambiguity," CESifo Working Paper Series 3727, CESifo.
  • Handle: RePEc:ces:ceswps:_3727
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    References listed on IDEAS

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    1. Gierlinger, Johannes & Gollier, Christian, 2008. "Socially Efficient Discounting under Ambiguity Aversion," IDEI Working Papers 561, Institut d'Économie Industrielle (IDEI), Toulouse.
    2. Peter Klibanoff & Massimo Marinacci & Sujoy Mukerji, 2005. "A Smooth Model of Decision Making under Ambiguity," Econometrica, Econometric Society, vol. 73(6), pages 1849-1892, November.
    3. Pindyck, Robert S., 2012. "Uncertain outcomes and climate change policy," Journal of Environmental Economics and Management, Elsevier, vol. 63(3), pages 289-303.
    4. Campbell, John Y, 1996. "Understanding Risk and Return," Journal of Political Economy, University of Chicago Press, vol. 104(2), pages 298-345, April.
    5. Klibanoff, Peter & Marinacci, Massimo & Mukerji, Sujoy, 2009. "Recursive smooth ambiguity preferences," Journal of Economic Theory, Elsevier, vol. 144(3), pages 930-976, May.
    6. Nengjiu Ju & Jianjun Miao, 2012. "Ambiguity, Learning, and Asset Returns," Econometrica, Econometric Society, vol. 80(2), pages 559-591, March.
    7. Michel Normandin & Pascal St-Amour, 1998. "Substitution, risk aversion, taste shocks and equity premia," Journal of Applied Econometrics, John Wiley & Sons, Ltd., vol. 13(3), pages 265-281.
    8. Plambeck, Erica L. & Hope, Chris & Anderson, John, 1997. "The model: Integrating the science and economics of global warming," Energy Economics, Elsevier, vol. 19(1), pages 77-101, March.
    9. Millner, Antony, 2013. "On welfare frameworks and catastrophic climate risks," Journal of Environmental Economics and Management, Elsevier, vol. 65(2), pages 310-325.
    10. Kelly, David L. & Kolstad, Charles D., 2001. "Malthus and Climate Change: Betting on a Stable Population," Journal of Environmental Economics and Management, Elsevier, vol. 41(2), pages 135-161, March.
    11. Weitzman, Martin L., 1998. "Why the Far-Distant Future Should Be Discounted at Its Lowest Possible Rate," Journal of Environmental Economics and Management, Elsevier, vol. 36(3), pages 201-208, November.
    12. Traeger, Christian P., 2010. "Intertemporal risk aversion – or – wouldn’t it be nice to tell whether Robinson Crusoe is risk averse?," CUDARE Working Paper Series 1102, University of California at Berkeley, Department of Agricultural and Resource Economics and Policy.
    13. Martin L. Weitzman, 2009. "On Modeling and Interpreting the Economics of Catastrophic Climate Change," The Review of Economics and Statistics, MIT Press, vol. 91(1), pages 1-19, February.
    14. Geoffrey Heal, 2009. "Climate Economics: A Meta-Review and Some Suggestions for Future Research," Review of Environmental Economics and Policy, Association of Environmental and Resource Economists, vol. 3(1), pages 4-21, Winter.
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    Citations

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    Cited by:

    1. Crost, Benjamin & Traeger, Christian P., 2013. "Optimal climate policy: Uncertainty versus Monte Carlo," Economics Letters, Elsevier, vol. 120(3), pages 552-558.
    2. Svenja Hector, 2013. "Accounting for Different Uncertainties: Implications for Climate Investments?," Working Papers 2013.107, Fondazione Eni Enrico Mattei.
    3. Iverson, Terrence, 2013. "Minimax regret discounting," Journal of Environmental Economics and Management, Elsevier, vol. 66(3), pages 598-608.
    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. 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.
    6. Svenja Hector(), "undated". "Accounting for Different Uncertainties: Implications for Climate Investments?," Working Papers ETH-RC-13-007, ETH Zurich, Chair of Systems Design.
    7. Larry S. Karp, 2012. "Provision of a Public Good with Altruistic Overlapping Generations and Many Tribes," CESifo Working Paper Series 3895, CESifo.

    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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