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ASSESSING UNCERTAINTY
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Global Climate Change Digest

A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 9, NUMBER 8, AUGUST 1996

PROFESSIONAL PUBLICATIONS...
ASSESSING UNCERTAINTY

Climatic Change, 33(2), June 1996, is devoted to "Assessing Uncertainty in Climate Change and Impacts" and contains the following five papers.


Item #d96aug15

"When Is It Appropriate to Combine Expert Judgments?" D.W. Keith (Dept. Chem., Harvard Univ., 12 Oxford St., Cambridge MA 02138; Internet: Keith@huarp.harvard.edu), 139-143.

This essay suggests an answer to the question by identifying the audience for the analysis and what they need, concluding that it is rarely appropriate to combine divergent expert judgments, as in "end-to-end" analyses (such as the Titus paper below). The core problem is that the fraction of experts who hold a given view is not proportional to the probability of that view being correct. Difficulty in combining expert opinion should serve as a warning to seek alternative modes of policy analysis.


Item #d96aug16

"Uncertainties in Global Climate Change Estimates," E. Paté-Cornell (Dept. Industrial Eng., Stanford Univ., Stanford CA 94305), 145-149.

Gives guidelines for using Bayesian probabilities when information on a problem is incomplete but policy decisions must be made. These represent a collective "degree of belief" in different hypotheses, given the evidence. Warns against using an adversarial process when resources are scarce and priorities must be set, because this is likely to lead to bad economic decisions and public policy failures.


Item #d96aug17

"The Risk of Sea Level Rise: A Delphic Monte Carlo Analysis in Which Twenty Researchers Specify Subjective Probability Distributions for Model Coefficients Within Their Respective Areas of Expertise," J.G. Titus (2122, US EPA, 401 M St. SW. Washington DC 20460; e-mail: titus@erols.com), V. Narayanan, 151-212.

Estimates the probabilities that sea level will rise by various amounts, using models employed in previous assessments, and the judgment of 20 experts in climatology and glaciology. Sea level rise by the year 2100 resulting from expected future temperature increase has a 50% chance of exceeding 34 cm, and a 1% chance of exceeding one meter. Tide gauge measurements indicate that sea level is rising about 1.8 mm/yr world wide; this analysis suggests that the contribution of greenhouse gases to this rise is 0.5 mm per year. If nonclimatic factors do not change, there is a 50 percent chance that global sea level will rise 45 cm by the year 2100. Discusses the advantages for other types of climate impact studies of using probability-based projections to incorporate the views of skeptics, the opinions of those who study empirical evidence, and the insights of climate modelers (which may be as useful as the model results themselves).


Item #d96aug18

"Uncertainty in Economic Models of Climate Change Impacts," D. Schimmelpfennig (Econ. Res. Service, Rm. 408, 1301 New York Ave. NW, Washington DC 20005), 213-234.

Uncertainty has been poorly represented in existing studies of climate change impacts. Reviews methods for characterizing uncertainty found in the literature and their limitations. Concludes that Monte Carlo type simulations are needed, in which randomness is apparent in a series of independent draws from a distribution suitably adjusted for climate change.


Item #d96aug19

"When We Don't Know the Costs or the Benefits: Adaptive Strategies for Abating Climate Change," R.J. Lempert (RAND, 1700 Main St., Santa Monica CA 90407), M.E. Schlesinger, S.C. Bankes, 235-274.

Most studies of climate change policy attempt to predict the greenhouse gas reduction plan that will have the optimum balance of long-term costs and benefits, but the large uncertainties involved render this approach unreliable. This study uses computational experiments on a linked system of climate and economic models to demonstrate the advantage of an adaptive strategy that can make midcourse corrections based on observations of the climate and economic systems. An adaptive strategy also provides an analytic framework for examining important policy and research issues that will probably arise in the future.

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