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Risk-adjusted gamma discounting

  • Weitzman, Martin L.

It is widely recognized that the economics of distant-future events, like climate change, is critically dependent upon the choice of a discount rate. Unfortunately, it is unclear how to discount distant-future events when the future discount rate itself is unknown. In previous work, an analytically-tractable approach called "gamma discounting" was proposed, which gave a declining discount rate schedule as a simple closed-form function of time. This paper extends the previous gamma approach by using a Ramsey optimal growth model, combined with uncertainty about future productivity, in order to "risk adjust" all probabilities by marginal utility weights. Some basic numerical examples are given, which suggest that the overall effect of risk-adjusted gamma discounting on lowering distant-future discount rates may be significant. The driving force is a "fear factor" from risk aversion to permanent productivity shocks representing catastrophic future states of the world.

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Article provided by Elsevier in its journal Journal of Environmental Economics and Management.

Volume (Year): 60 (2010)
Issue (Month): 1 (July)
Pages: 1-13

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Handle: RePEc:eee:jeeman:v:60:y:2010:i:1:p:1-13
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  1. Weitzman, Martin L., 2009. "Additive Damages, Fat-Tailed Climate Dynamics, and Uncertain Discounting," Economics Discussion Papers 2009-26, Kiel Institute for the World Economy.
  2. Newell, Richard G. & Pizer, William A., 2004. "Uncertain discount rates in climate policy analysis," Energy Policy, Elsevier, vol. 32(4), pages 519-529, March.
  3. Gollier, Christian & Weitzman, Martin L., 2010. "How should the distant future be discounted when discount rates are uncertain?," Economics Letters, Elsevier, vol. 107(3), pages 350-353, June.
  4. 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.
  5. 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.
  6. Partha Dasgupta, 2008. "Discounting climate change," Journal of Risk and Uncertainty, Springer, vol. 37(2), pages 141-169, December.
  7. William D. Nordhaus, 2007. "A Review of the Stern Review on the Economics of Climate Change," Journal of Economic Literature, American Economic Association, vol. 45(3), pages 686-702, September.
  8. GOLLIER Christian, 2008. "Should we discount the far-distant future at its lowest possible rate?," LERNA Working Papers 08.30.274, LERNA, University of Toulouse.
  9. Martin L. Weitzman, 1998. "Gamma Discounting," Harvard Institute of Economic Research Working Papers 1843, Harvard - Institute of Economic Research.
  10. Ekaterini Panopoulou & B. Groom & P. Koundouri & Theologos Pantelidis, 2005. "Discounting the distant future: How much does model selection affect the certainty equivalent rate?," Economics, Finance and Accounting Department Working Paper Series n1480105, Department of Economics, Finance and Accounting, National University of Ireland - Maynooth.
  11. Hepburn, Cameron & Groom, Ben, 2007. "Gamma discounting and expected net future value," Journal of Environmental Economics and Management, Elsevier, vol. 53(1), pages 99-109, January.
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