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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.

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Bibliographic Info

Paper provided by CESifo Group Munich in its series CESifo Working Paper Series with number 3727.

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Date of creation: 2012
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Handle: RePEc:ces:ceswps:_3727

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

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References

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  1. Ghirardato, Paolo & Maccheroni, Fabio & Marinacci, Massimo, 2004. "Differentiating ambiguity and ambiguity attitude," Journal of Economic Theory, Elsevier, vol. 118(2), pages 133-173, October.
  2. John Y. Campbell, 1993. "Understanding Risk and Return," NBER Working Papers 4554, National Bureau of Economic Research, Inc.
  3. Azfar, Omar, 1999. "Rationalizing hyperbolic discounting," Journal of Economic Behavior & Organization, Elsevier, vol. 38(2), pages 245-252, February.
  4. Maccheroni, Fabio & Marinacci, Massimo & Rustichini, Aldo, 2006. "Dynamic variational preferences," Journal of Economic Theory, Elsevier, vol. 128(1), pages 4-44, May.
  5. Normandin, Michel & St-Amour, Pascal, 1996. "Substitution, Risk Aversion, Taste Shocks and Equity Premia," Cahiers de recherche 9606, Université Laval - Département d'économique.
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  13. Peter Klibanoff & Massimo Marinacci & Sujoy Mukerji, 2002. "A smooth model of decision making under ambiguity," ICER Working Papers - Applied Mathematics Series 11-2003, ICER - International Centre for Economic Research, revised Apr 2003.
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  15. Ju, Nengjiu & Miao, Jianjun, 2009. "Ambiguity, Learning, and Asset Returns," MPRA Paper 14737, University Library of Munich, Germany, revised Apr 2009.
  16. 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.
  17. Kihlstrom, Richard E. & Mirman, Leonard J., 1974. "Risk aversion with many commodities," Journal of Economic Theory, Elsevier, vol. 8(3), pages 361-388, July.
  18. Gierlinger, Johannes & Gollier, Christian, 2008. "Socially Efficient Discounting under Ambiguity Aversion," IDEI Working Papers 561, Institut d'Économie Industrielle (IDEI), Toulouse.
  19. Peter Klibanoff & Massimo Marinacci & Sujoy Mukerji, 2006. "Recursive Smooth Ambiguity Preferences," Carlo Alberto Notebooks 17, Collegio Carlo Alberto, revised 2008.
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  22. Gollier, Christian, 2002. "Discounting an uncertain future," Journal of Public Economics, Elsevier, vol. 85(2), pages 149-166, August.
  23. 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.
  24. Martin L. Weitzman, 2007. "A Review of the Stern Review on the Economics of Climate Change," Journal of Economic Literature, American Economic Association, vol. 45(3), pages 703-724, September.
  25. Ravi Bansal & Amir Yaron, 2000. "Risks for the Long Run: A Potential Resolution of Asset Pricing Puzzles," NBER Working Papers 8059, National Bureau of Economic Research, Inc.
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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. Iverson, Terrence, 2013. "Minimax regret discounting," Journal of Environmental Economics and Management, Elsevier, vol. 66(3), pages 598-608.
  3. 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.
  4. Traeger, Christian, 2012. "A 4-stated DICE: quantitatively addressing uncertainty effects in climate change," Department of Agricultural & Resource Economics, UC Berkeley, Working Paper Series qt6jx2p7fv, Department of Agricultural & Resource Economics, UC Berkeley.
  5. Larry S. Karp, 2012. "Provision of a Public Good with Altruistic Overlapping Generations and Many Tribes," CESifo Working Paper Series 3895, CESifo Group Munich.
  6. Svenja Hector(), . "Accounting for Different Uncertainties: Implications for Climate Investments?," Working Papers ETH-RC-13-007, ETH Zurich, Chair of Systems Design.
  7. Traeger, Christian, 2013. "A 4-stated DICE: quantitatively addressing uncertainty effects in climate change," Department of Agricultural & Resource Economics, UC Berkeley, Working Paper Series qt9034k05t, Department of Agricultural & Resource Economics, UC Berkeley.
  8. Svenja Hector, 2013. "Accounting for Different Uncertainties: Implications for Climate Investments?," Working Papers 2013.107, Fondazione Eni Enrico Mattei.

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