建構全球可耕地利用變動及相關溫室氣體排放之可計算一般均衡模型

Abstract

本計畫旨在運用Lee et al. (2008)所建構之土地利用及其相關之溫室氣體排放量資料 來建立一土地利用及土地利用相關之溫室氣體排放之全球可計算一般均衡模型。我 們採用聯合國之國際糧食及農業組織(The Food and Agriculture Organization of the United Nations)所開發之「農業生態區」(agro-ecological zoning)的方法，將一國的可 耕地面區分為六區類。在同一農業生態區下的土地之作物生長條件(例如：土質、 土壤酸鹼值、地形、溫度、降雨量)類似。我們按土地所在區位之土壤及氣候條件 所能支持作物一年中的生長日數區分為六類農業生態區，分別是0 天至59 天，60 天至119 天，.....，300 天至360 天等六類。農作物種植、牲畜的畜養及林地等土地 利用活動按其所需之作物生長條件分佈於這六個農業生態區中。本計畫將建立一土 地利用及溫室氣體排放之全球可計算一般均衡模型，並以其模擬政策或其他經濟變 數的變動（例如：碳稅的課徵、新興經濟體的糧食需求增加）對土地利用及土地利 用活動相關之溫室氣體排放的影響。

The project aims to model land use change and land-based emissions in a global computable general equilibrium model, the GTAP model, with the GTAP Land Use and Greenhouse Gases Emissions data base, for Integrated Assessment of climate change policies. We follow the agro-ecological zoning methodology as developed by the Food and Agriculture Organization of the United Nations to identify lands located in six zones. Lands located in a specific AEZ have similar soil, landform and climatic characteristics. The six AEZs range over a spectrum of length of growing period (LGP) for which their climate characteristics can support for crop growing. AEZ 1 covers the land of the temperature and moisture regime that is able to support LGP up to 60 days per annum. On the other end of the LGP spectrum, lands in AEZ 6 can support a LGP from 270 to 360 days per annum. Crop growing, livestock breeding, and timber plantation are dispersed on lands of each AEZ of the six, whichever meets their climatic and edaphic requirements. In the new model to be built in this project, we will assume that land located in a specific AEZ can be moved only between sectors that the land is appropriate for their use. That is, land is mobile between crop, livestock and forestry sectors within, but not across, AEZ’s. In the standard GTAP model, land is assumed to be transformable between uses of crop growing, livestock breeding, or timber plantation, regardless of climatic or soil constraints. The fact is that most crops can only grow on lands that is under certain temperature, moisture, soil type, land form, etc.. The same concern arises for land use by the livestock and the forestry sectors. Lands that are suitable for growing wheat may not be good for rice cultivation alike, even under transformation at a reasonable cost. The introduction of the agro-ecological zoning in GTAP helps to clear up the counterfactual assumption in inter-sectoral land transition, and permit a sound presentation of sectoral competition for land.