Forest carbon prospecting for climate change mitigation: Version 1.0

This data package includes the two 1-km resolution global maps (.tif) of tropical forests between ~23.44°N and 23.44°S produced from the study: 1) investible forest carbon (in tCO₂e ha^-1y^-1) and 2) forest carbon return-on-investment (Net Present Value in USD ha^-1y^-1) over a 30-year timeframe. It also includes the R script to reproduce these layers and their uncertainties. <em><strong>Investible Forest Carbon</strong>: </em>The investible forest carbon map was produced based on the total volume of CO₂e associated with the three main carbon pools in the tropics, namely aboveground carbon, belowground carbon and soil organic carbon. This is followed by the application of key Verified Carbon Standard (VCS) criteria including additionality, to determine the magnitude and areas of investible forest carbon across the tropics. <em>Aboveground carbon.</em> A stoichiometric factor of 0.475 was applied to recent spatial data on aboveground carbon biomass to obtain carbon stock based on established carbon accounting methodologies. An uncertainty analyses was also performed to account for potential variability in stoichiometric factor. Subsequently, a conversion factor of 3.67 was applied to the carbon stock layer to obtain the volume of CO₂e associated with this carbon pool. <em>Belowground carbon</em>. Belowground carbon biomass was firstly derived by applying two allometric equations relating to root to shoot biomass to the most recent spatial dataset on aboveground carbon biomass following established carbon accounting methodologies. The two equations are: Belowground biomass = 0.489×aboveground biomass^0.89; and Belowground biomass = 0.26×aboveground biomass A stoichiometric factor of 0.475 was subsequently applied to the estimated belowground carbon biomass to obtain the carbon stock. An uncertainty analyses was then performed to determine the mean, minimum and maximum values for belowground carbon. Following that, a conversion factor of 3.67 was applied to the carbon stock layer to obtain the volume of CO₂e associated with this carbon pool. <em>Soil Organic Carbon</em>. Organic carbon density of the topsoil layer (0-30 cm) was obtained from the European Soil Data Centre as it represented the best data available for soil organic carbon. A conversion factor of 3.67 was subsequently applied to derive the volume of CO₂e associated with this carbon pool. <em>Applying VCS criteria</em>. The criterion of additionality is a pre-condition for carbon credits to be certified under the VCS. This implies that only the volume of forest carbon that are under imminent threat of decline or loss if left unprotected by a conservation intervention can be certified under the VCS. The volume of forest carbon under threat of loss was based on the best available data on predicted deforestation rates across the tropics (through to the year 2029), and annualized over predicted 15-year period. The estimated annual deforestation rates was then applied to the total volume of CO₂e associated with tropical forests as estimated above, deriving the volume of CO₂e that would be certifiable and thus investible under the VCS. In addition, a conservative 10-year decay estimate was assumed for the estimate of the belowground carbon pool, and lands that will likely not be certifiable for other reasons, including recently deforested areas (i.e. for the period of 2010-2017), a well as human settlements, were excluded. Lastly, the VCS requirement to set aside buffer credits of 20% was accounted for to consider the risk of non-permanence associated with Agriculture, Forestry and Other Land Use (AFOLU) projects. <strong><em>Return</em>-<em>on-Investment</em></strong>. From the investible forest carbon map, the relative profitability of these areas was then modelled to produce a global forest carbon return-on-investment map based on their NPV. The NPV of returns were based on several simplifying assumptions following established values from previous studies. <em>Cost of project establishment</em>. The cost of project establishment was estimated to be at $25 ha^-1. This was based on a range of costs that are key to the development of a project, including but not limited to project design, governance and planning, enforcement, zonation, land tenure and acquisition, surveying and research. <em>Cost for annual maintenance</em>. The cost for annual maintenance was estimated to be $10 ha^-1, which included aspects such as in education and communication, monitoring, sustainable livelihoods, marketing, finance and administration. <em>Carbon price</em>. A constant carbon price of $5.8 t^-1CO­₂e for the first five years was applied. This price was based on an average price of carbon for avoided deforestation projects reported recently by Forest Trends’ Ecosystem Marketplace (i.e. for the period 2006 – 2018). Subsequently, a 5% price appreciation was applied annually over a project timeframe of 30 years. <em>Discount rate</em>. We calculated NPV of annual and accumulated profits over 30 years based on a 10% risk-adjusted discount rate. Further details for these datasets and their uncertainties are presented in Koh et. al. For questions or issues on the spatial data layers, please contact Yiwen Zeng ([e-mail]).本数据包包含两份分辨率为1公里的热带森林全球栅格地图（.tif格式），覆盖范围介于北纬约23.44°至南纬23.44°之间，基于本研究生成，具体包括：1）可投资森林碳储量（单位：吨二氧化碳当量每公顷每年，tCO₂e ha⁻¹y⁻¹）；2）30年时间尺度下的森林碳投资回报率（以美元计价的净现值，单位：USD ha⁻¹y⁻¹）。此外，数据包还包含用于复现上述图层及其不确定性的R脚本。 **可投资森林碳**：可投资森林碳地图基于热带地区三大主要碳库（即地上碳库、地下碳库与土壤有机碳库）对应的总二氧化碳当量体积生成。随后应用经核证碳标准（Verified Carbon Standard, VCS）的关键准则，包括额外性原则，以确定全球热带地区可投资森林碳的规模与分布区域。 **地上碳**：基于已确立的碳核算方法学，对最新的地上碳生物量空间数据应用0.475的化学计量系数，以计算碳储量。同时开展不确定性分析，以覆盖化学计量系数可能存在的变异性。随后，对碳储量图层应用3.67的转换系数，以得到该碳库对应的二氧化碳当量体积。 **地下碳**：遵循已确立的碳核算方法学，首先通过两个根冠生物量异速生长方程，基于最新的地上碳生物量空间数据集推导地下碳生物量。两个方程分别为：地下生物量 = 0.489×地上生物量^0.89；以及地下生物量 = 0.26×地上生物量。随后对估算得到的地下碳生物量应用0.475的化学计量系数，以计算碳储量。随后开展不确定性分析，以确定地下碳储量的均值、最小值与最大值。之后，对碳储量图层应用3.67的转换系数，以得到该碳库对应的二氧化碳当量体积。 **土壤有机碳**：表层土壤（0-30 cm）的有机碳密度取自欧洲土壤数据中心（European Soil Data Centre），因其为现有土壤有机碳最佳数据源。随后应用3.67的转换系数，以得到该碳库对应的二氧化碳当量体积。 **应用VCS准则**：额外性原则是碳信用额获得VCS认证的前置条件。这意味着，只有在未采取保护干预措施的情况下面临退化或丧失紧迫威胁的森林碳体量，才可获得VCS认证。面临丧失威胁的森林碳体量基于热带地区最新的预测毁林率数据（截至2029年）计算，并按预测的15年周期年化。将估算得到的年化毁林率应用于前文估算的热带森林总二氧化碳当量体积，即可得到符合VCS认证标准、具备投资价值的二氧化碳当量体量。此外，本次分析假设地下碳库存在10年的保守衰减估算，同时排除了因其他原因无法获得认证的区域，包括2010-2017年期间新近毁林区域以及人类定居点。最后，考虑到农业、林业与其他土地利用（Agriculture, Forestry and Other Land Use, AFOLU）项目存在的非持久性风险，纳入了VCS要求预留20%缓冲信用额的规则。 **投资回报率**：基于可投资森林碳地图，对这些区域的相对盈利能力进行建模，以净现值（Net Present Value, NPV）为核心指标生成全球森林碳投资回报率地图。收益的净现值计算基于多项简化假设，参考了过往研究中的既定参数。 **项目设立成本**：项目设立成本估算为25美元每公顷（$25 ha⁻¹）。该估算基于项目开发所需的多项关键成本，包括但不限于项目设计、治理与规划、执法、分区、土地权属与获取、勘测与研究。 **年度维护成本**：年度维护成本估算为10美元每公顷（$10 ha⁻¹），涵盖教育与宣传、监测、可持续生计、营销、财务与行政等方面。 **碳价格**：前五年采用固定碳价格5.8美元每吨二氧化碳当量（$5.8 t⁻¹CO₂e），该价格基于Forest Trends旗下Ecosystem Marketplace近期报告的毁林避免项目碳平均价格（2006-2018年期间）。随后，在30年的项目周期内，碳价格每年按5%的幅度升值。 **贴现率**：基于10%的风险调整贴现率，计算了30年内年度利润与累计利润的净现值。 关于上述数据集及其不确定性的更多细节详见Koh等人的研究。若对空间数据图层有疑问或问题，请联系曾怡雯（[e-mail]）。