報告書番号

Y94012

タイトル（和文）

地球温暖化によるグローバル損害コスト評価の現状

タイトル（英文）

CURRENT STATUS OF GLOBAL WARMING DAMAGE COSTS ASSESSMENT

概要 （図表や脚注は「報告書全文」に掲載しております）

地球温暖化による世界全体の損害コスト評価の現状を調査した。産業革命前に比較して大気中のＣＯ２濃度が倍増した場合を想定して行われた積み上げ評価によると，世界全体での損害はＧＮＰの１％程度という結果でおおむね一致を見ているが，これらの評価は，（１）経済的波及効果の無視，（２）過度的変化の無視，（３）情報不足のために先験的仮定が多い，などの問題点のため概数評価に留まっている。また損害コストには地域格差があり，それは（１）支払い意志額，（２）産業構造，（３）気候変動影響の地域ごとの特性，の違いを反映している。特に途上国はその損害コストが高く，ＧＮＰ比にして先進国の数倍に達し得ると考えられている。ＣＯ２濃度倍増時に損害コストがＧＮＰの約１％に達するという仮定のもとに現時点の石油火力発電によるＣＯ２排出損害コストを算出すると，それは最大で１－３円／ｋＷｈ程度であり，割引率の選択によってはその十分の一

概要 （英文）

THIS PAPER EXAMINES SEVERAL BENCHMARK STUDIES ON GLOBAL WARMING DAMAGE COSTS DUE TO THE DOUBLING OF ATMOSPHERIC CO2LEVELS FROM THE PRE-INDUSTRIAL LEVEL(280PPM).IT SUMMARIZES THE METHODOLOGIES,MAJOR RESULTS,AND LIMITATIONS OF STATE-OF-THE-ART EVALUATION TECHNIQUES. A MODEL FOR CALCULATING MARGINAL DAMAGE COSTS DUE TO CO2 EMISSION AT PRESENT IS ALSO DEMONSTRATED AS AN APPLICATION OF THE BENCHMARK STUDIES. THE DISPUTE ABOUT DISCOUNT RATE,WHICH IS THE MOST CRUCIAL PARAMETER IN THE CALCULATION,IS SUMMARIZED AS AN APPENDIX. THE MAJOR FINDINGS FROM THE BENCHMARK STUDIES ARE AS FOLLOWS. (A)THERE IS A CONSENSUS THAT DOUBLING CO2 CONCENTRATION CAUSES A LOSS OF ABOUT 1% OF WORLD TOTALGNP. THE LOSS TO DEVELOPING COUNTRIES TENDS TO BE HIGHER THAN THAT TO DEVELOPED COUNTRIES IN TERMS OF PERCENTAGE OF GNP. (B)DAMAGE COSTS DISPARITIES BETWEEN REGIONS OCCUR MAINLY FOR THREE REASONS:(1)WILLINGNESS-TO-PAY DIFFERENCES BETWEEN RICH AND POOR COUNTRIES;(2)DIFFERENCES IN INDUSTRIAL STRUCTURE;(3)UNEVEN NATURE OF CLIMATE CHANGE. (C)THESE BENCHMARK STUDIES ARE NOT MORE THAN ORDER-OF-MAGNITUDE ESTIMATES,SO THE RESULTSSHOULD NOT BE TAKEN AS ACCURATE. MAJOR DRAWBACKS OF THE ESTIMATES INCLUDE:NEGLECT OF INDIRECT ECONOMIC EFFECTS,NO CONSIDERATION OF TRANSIENT RESPONSE,AND MANY AD-HOC ASSUMPTIONS. ASSUMING A 1% LOSS TO GNP CAUSED BY DOUBLING CO2 CONSENTRATION,THE MARGINAL DAMAGE COSTS OF CO2 EMISSIONFROM AN OIL-FIRED POWER PLANT ARE CALCULATED TO BE 1-3 CENTS/KWH AT A ZERO UTILITY DISCOUNT RATE,AND1/10 OR LESS AT A 3% UTILITY DISCOUNT RATE. THERE IS NO DOUBT THAT QUANTIFYING GLOBAL WARMING DAMAGE IS IN DISPENSABLE,BUT IT IS DIFFICULT TO FORMULATE AN ECONOMICALLY-EFFICIENT GREENHOUSE-GAS COUNTROL POLICY. MOREOVER,THE UNCERTAINTY OF NO LESS THAN 50%SUGGESTED BY FANKHAUSER WILL NEVER BE REMOVED,HOWEVER THE VAST RESOURCES AND TIME DUE TO FORMIDABLE UN-CERTAINTIES. THUS,POLICY MAKERS SHOULDNOT ONLY TAKE THE CENTRAL VALUE OF COST ESTIMATES INTO ACCOUNT,BUT SHOULD TAKE A VARIETY OF UNCERTAINTIES INT

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