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Economics 331 1 Finale on climate change policy Today: Endgame Alternative perspectives • Environmentalist perspective • Conservative perspective • Reprise on learning • Tipping points and policy 2 Endgame for course 1. Final exam (absence by Dean’s excuse only) ECON 331. Assigned to exam group 33 Friday, May 6, 2011. 9:00 am – 11:00 am 2. Structure: probably three parts: will probably have choice. 40 minutes for “prepared questions” (to be posted); 40 minutes problems; 40 minutes more problems 3. I will post last year’s exams (but no answers) 4. Review sessions: WN 1 next week; WN 1 week after; office hours by Lint 5. Grades will be approximately based 20 percent on the problems, 30 percent on the paper, 20 percent on the midterm, and 30 percent on the final, all with adjustments. 6. Paper due noon April 27 (hard copy outside my office; electronic copies to WN and LB) 7. Hard deadlines for seniors. No postponements for last-minute procrastinations. 3 The spectrum of economic views on climate change Strong --------- Stern ------------------A----B----C----------DICE------D-----------Lomberg--- Weak policies $100 /tCO2 $10 - $20/tCO2 $1/tCO2 policies Stern: Stern Review, also summarized in his Ely lecture, American Economic Review. Lomberg has organized the Copenhagen consensus of (largely) conservative thinkers to rank major issues. A, B, C, D are other models 4 The Copenhagen Consensus: Priorities for Action “In ordering the proposals, the panel was guided predominantly by consideration of economic costs and benefits.” http://www.copenhage nconsensus.com Economics 487b, Spring 2007 5 Environmentalist critique Stern/Krugman critique* of the DICE model approach: 1. Uses too high a discount rate 2. Ignores the uncertainty and the “fat tail” of lowprobability catastrophic outcomes 3. Uses a temperature sensitivity coefficient of 3 °C per CO2 doubling instead of more realistic 6 °C Next slide shows the sensitivity of the emissions control rate if we introduce these sequentially. Which are most important? *Stern Review : http://webarchive.nationalarchives.gov.uk/+/http://www.hmtreasury.gov.uk/sternreview_index.htm Krugman, “Building a Green Economy,” NYT Magazine, 2010, http://www.nytimes.com/2010/04/11/magazine/11Economy-t.html 6 Emissions Controls for Environmentalist Assumptions 1.0 Emissions control rate 0.9 0.8 Optimal: base assumptions 0.7 6 deg C 0.6 6 deg C and double damages 0.5 Base and low discounting 0.4 6 °C and low discounting 0.3 6 deg C, double damages, and low discounting 0.2 0.1 0.0 2005 2025 2045 2065 2085 2105 7 Reprise on learning 8 Original example The state of the environmental world Good outcome (low damage, many green technologies) Climate policy Poor outcome (catastrophic damage, no green technologies) Strong policies (high carbon tax, cooperation, R&D) -1% -1% Weak policies (no carbon tax, strife, corruption) 0% -50% 90% 10% Probability Learn then act: E(U) = 0.9 x 0% + 0.1 x -1% = -0.1% Expectation of strong = 0.1 Act then learn: Strong: E(U) = 0.9 x -1% + 0.1 x -1% = -1% Best policy: Expectation of strong = 1 Weak: E(U) = 0.9 x 0% + 0.1 x -50% = -5% Therefore, learning leads to weaker policies. Precautionary motive holds. 9 Revised example with lower damage in bad state. The state of the environmental world Good outcome (low damage, many green technologies) Climate policy Poor outcome (catastrophic damage, no green technologies) Strong policies (high carbon tax, cooperation, R&D) -1% -1% Weak policies (no carbon tax, strife, corruption) 0% -5% 90% 10% Probability Learn then act: E(U) = 0.9 x 0% + 0.1 x -1% = -0.1% Expectation of strong = 0.1 Act then learn: Strong: E(U) = 0.9 x -1% + 0.1 x -1% = -1.0% Weak: E(U) = 0.9 x 0% + 0.1 x -5% = -0.5% Best policy: Expectation of strong = 0 Therefore, learning leads to stronger policies. Precautionary motive DOES NOT hold. 10 Conclusion Example shows how expected strength of policy can either go up or down with learning. No general theorem about whether learning increases or decreases your abatement (or investments more generally) 11 How can we treat tipping points and threshold effects? 12 OOPS!!!!!!! k 13 k* k** k*** Note: Have new and different locally stable equilibrium 14 k* k** k k*** Non-linearities in the climate system Most of the impacts literature examines gradual climate change, with roughly linear systems and impacts. Scientists have been particularly concerned about discontinuities, abrupt climate change, tipping points, catastrophic impacts. How can we deal with thresholds in our economic analysis? A very tough problem on the frontier. Examples from climate system 16 Source: Lenton et al., “Tipping Elements,” PNAS, Feb 2008, 1786. Optimum Without Thresholds Total Damage Total Abatement Cost 0 Temperature* Temperature 17 17 Optimum With Thresholds Total Damage Total Abatement Cost 0 Temperature* Temperature 18 18 Optimum Without Thresholds Marginal Abatement Cost 0 Marginal Damage Temperature* Temperature 19 19 Optimum With Thresholds ???!!!??? Marginal Abatement Cost 0 Marginal Damage Temperature* Temperature 20 20 Net income 0 Which is the real maximum? Temperature 21 21 Have multiple equilibrium for system and policy • DICE type model. • Catastrophic damage at 3 °C = 50 % of output • Have abatement choice about whether to pass the threshold as function of costs and benefits. • Abatement cost varies from 1% to 100% of output. • Next slide shows whether optimally pass the threshold as function of abatement cost. • Note that SOLVER can’t reliably get the right answer near the cross-over because it is local optimizer! 22 Solutions for temperature 14 Maximum temperature (deg C) 12 Max T from upper end Cross catastrophic threshold Max T from lower end 10 8 6 4 2 Avoid catastrophic threshold 0 0 0.2 0.4 0.6 0.8 1 1.2 Mitigation cost intercept Note: 1. Have algorithm problems because multiple local maxima. 2. Sharp discontinuity in solution around threshold. 23 Solutions for PV net income 12000 Avoid catastrophic threshold Present value net output 10000 8000 6000 Cross catastrophic threshold 4000 PV from upper end PV from lower end 2000 0 0 0.2 0.4 0.6 0.8 1 Mitigation cost intercept 24 Note: Solution is continuous for PV income (although bad) 1.2 Solutions for first-period control rate 0.900 Emissions control rate first period 0.800 Avoid catastrophic threshold 0.700 0.600 0.500 Note: had slightly wrong graph in class. 0.400 0.300 Cross catastrophic threshold 0.200 0.100 0 0.2 0.4 0.6 0.8 1 1.2 Mitigation cost intercept Note: Paradox that control rate goes UP around switch point. Why? First you speed up, then when you know you are going to miss your plane, slow down. 25 Where do we go from here? It is in YOUR hands… 26