Expected Utility and Catastrophic Risk in a Stochastic Economy-Climate ModelIkefuji, M.; Laeven, R.J.A.; Magnus, J.R.; Müris, C.H.M.
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Chris MurisCentER, Tilburg University * We are grateful to Graciela Chichilnisky, John Einmahl, Reyer Gerlagh, Johan Eyckmans, Sjak Smulders, Peter Wakker, Aart de Zeeuw, Amos Zemel, and seminar participants at the Tilburg Sustainability Center for helpful comments. This research was funded in part by the JSPS under grant C-22530177 (Ikefuji) and by the NWO under grant Vidi-2009 (Laeven). E-mail addresses: ikefuji@iser.osaka-u.ac.jp (Ikefuji), r.j.a.laeven@uvt.nl (Laeven), magnus@uvt.nl (Magnus), chrismuris@gmail.com (Muris). Abstract: In the context of extreme climate change, we ask how to conduct expected utility analysis in the presence of catastrophic risks. Economists typically model decision making under risk and uncertainty by expected utility with constant relative risk aversion (power utility); statisticians typically model economic catastrophes by probability distributions with heavy tails. Unfortunately, the expected utility framework is fragile with respect to heavy-tailed distributional assumptions. We specify a stochastic economyclimate model with power utility and explicitly demonstrate this fragility. We derive necessary and sufficient compatibility conditions on the utility function to avoid fragility and solve our stochastic economy-climate model for two examples of such compatible utility functions. We further develop and implement a procedure to learn the input parameters of our model and show that the model thus specified produces quite robust optimal policies. The numerical results indicate that higher levels of uncertainty (heavier tails) lead to less abatement and consumption, and to more investment, but this effect is not unlimited.JEL Classification: D81; Q5.