考慮機會成本下碳吸存成本效益之經濟分析

On the Cost-Benefit Analysis of Carbon Sequestration under Considering Opportunity Cost

為因應溫室氣體排放量增加所造成對人類社會之不利影響，近年來世界各國均積極採取各種方式來降低溫室氣體之排放量，其中增加森林碳吸存被視為是成本較低的減量策略。森林碳匯為京都議定書中減緩氣候變化機制之一，在京都議定書中第3.3條及第3.4條均提到造林與森林管理活動產生之碳吸存均可併入排放減量值。因此，造林之碳吸存量與碳吸存成本效益分析乃為目前攸關政策擬定之研究議題。本研究以蓮華池研究中心之杉木人工林為例，分析杉木造林之碳吸存成本與效益。本研究發現前人文獻並未將木材收益列入碳吸存之機會成本一部份，因此可能產生低估造林碳吸存成本之情形。根據本研究之實證模擬，其主要結果顯示，在考慮碳吸存之機會成本後，20年生之杉木人工林，其每公頃碳吸存量為54.22噸，碳吸存效益現值為每公頃54,154.85元，木材收益現值為每公頃225,931.69元，累積碳吸存成本為每公頃226,808.69元，單位碳吸存成本為每噸4,183.28元。在考慮碳吸存之機會成本後，則平均單位碳吸存成本在2,253.78元至2,866.42元之問，為求嚴謹，本研究另考慮三種碳釋放比率來計算單位碳吸存成本，估計結果為在離散價格函數設定下，每噸碳吸存成本介於362元至3,279.25元之問，在連續價格函數設定下，每噸碳吸存成本介於898.20元至5,309.86元之問本研究之估算結果與國外文獻計算的碳吸存成本大致相符。

In order to reduce the negative impact due to the climate change resulting from increasing greenhouse gases, many countries in the world have actively adopted various kinds of approaches to reduce greenhouse gas emissions. Among those the forest carbon sink/sequestration has been regarded as one of the strategies which can provide the lowest costs for the reduction of emissions. Since forests are increasingly recognized as playing a key role in reducing carbon dioxide, forest carbon sinks have been included in Kyoto protocol as one of the mechanisms in mitigating climate change. According to Kyoto Protocol Article 3.3 and 3.4, the production of CO2 sequestration and emission due to the strategies, which includes increasing afforestation, reforestation, deforestation (ARD) and improving forest management, can be merged to the amount of national emissions reduction. Concerning the economics of a country, forest management is a good cost-effective strategy for carbon reduction. The aim of this paper is to assess the economic cost and benefit of carbon reduction under China Fir plantation at Lien-Hua-Chih. In this research, we found that profits from harvest of timber have not been taken into consideration as part of the opportunity costs of carbon sequestration in previous studies, which may have caused underestimation of the carbon sequestration cost of human-made forest plantations. Based on the results of empirical simulation conducted in this research, a 20-year-old China Fir plantation yields a carbon sequestration volume of 54.22 tons after the opportunity costs are taken into consideration. Each hectare yields a present value of benefit of NT54,154.85 from carbon sequestration and NT225,931.69 from timber harvest. And each hectare incurs an accumulated carbon sequestration cost of NT226,808.69, and the unit carbon sequestration cost comes to NT4,183.28/ton. After factoring in the opportunity costs of carbon sequestration, the average unit cost of carbon sequestration rises from NT2,253.78 to NT2,866.42. To be thorough, this research brought in three additional carbon release ratios to calculate the unit carbon sequestration cost. Results show that, under the configuration of dispersed price function, the per-ton cost of carbon sequestration falls between NT362 and NT3,279.25, and when configured under continuous price function, the per-ton carbon sequestration cost falls between NT898.20 and NT5,309.86. Estimates derived from this research are generally consistent to the carbon sequestration costs estimated in the previous studies published internationally.