Forest greenhouse gas emissions

Overview This emissions layer is part of the forest carbon flux model described in Harris et al. (2021). This paper introduces a geospatial monitoring framework for estimating global forest carbon fluxes which can assist a variety of actors and organizations with tracking greenhouse gas fluxes from forests and in decreasing emissions or increasing removals by forests. Forest carbon emissions represent the greenhouse gas emissions arising from stand-replacing forest disturbances that occurred in each modeled year (megagrams CO2e emissions/ha, between 2001 and 2025). Emissions include all relevant ecosystem carbon pools (aboveground biomass, belowground biomass, dead wood, litter, soil organic carbon) and greenhouse gases (CO2, CH4, N2O). Emissions estimates for each pixel are calculated following IPCC Guidelines for national greenhouse gas inventories where stand-replacing disturbance occurred, as mapped in the Global Forest Change annual tree cover loss data of Hansen et al. (2013). The carbon emitted from each pixel is based on carbon densities in 2000, with adjustment for carbon accumulated between 2000 and the year of disturbance. Emissions reflect a gross estimate, i.e., carbon removals from subsequent regrowth are not included. Instead, gross carbon removals resulting from subsequent regrowth after clearing are accounted for in the companion forest carbon removals layer. The fraction of carbon emitted from each pixel upon disturbance (emission factor) is affected by several factors, including the direct driver of disturbance, whether fire was observed in the year of or preceding the observed disturbance event, whether the disturbance occurred on peat, and more. All emissions are assumed to occur in the year of disturbance. Emissions can be assigned to a specific year using the Hansen tree cover loss data; separate rasters for emissions for each year are not available from GFW. All input layers were resampled to a common resolution of 0.00025 × 0.00025 degrees each to match Hansen et al. (2013). We have made several updates to the model since its original release. For documentation through the current version, please refer to this blog. For a more detailed description of the changes included through the 2023 tree cover loss launch (released spring 2024) and a comparison of the model's fluxes with those from the Global Carbon Budget and national greenhouse gas inventories, please refer to this article. Three variations of emissions rasters are available for download: megagrams CO2e emissions/ha in pixels with >30% tree cover density (TCD) in 2000 or tree cover gain: Used for visualizing (mapping) emissions according to the default GFW TCD threshold because it represents the density of emissions per hectare. You would use this if you want to only include emissions in pixels that are more conservatively defined as forest. megagrams CO2e emissions/pixel in pixels with >30% TCD in 2000 or tree cover gain: Used for calculating the emissions in an area of interest (AOI) according to the default GFW TCD threshold because the values of the pixels in the AOI can be summed to obtain the total emissions for that area. You would use this if you want to only include emissions in pixels that are more conservatively defined as forest. megagrams CO2e emissions/pixel in pixels with any amount of tree cover in 2000 or tree cover gain: Used for calculating the emissions in an area of interest (AOI) without any TCD threshold because the values of the pixels in the AOI can be summed to obtain the total emissions for that area. This would represent the total emissions from tree cover loss in the AOI without applying a TCD threshold. You would use this if you want to include emissions in pixels that have low (<30%) TCD in 2000. The values in the megagrams CO2e/pixel layers were calculated by adjusting the emissions per hectare by the size of each pixel, which varies by latitude. Tree cover density in 2000 is according to Hansen et al. (2013) and tree cover gain between 2000 to 2020 is according to Potapov et al. (2022) Related Open Data Portal layers: Forest Carbon Removals, Net Forest Carbon Flux Google Earth Engine: asset (megagrams CO2e emissions/ha in pixels with >30% TCD) and visualization script Resolution: 30 x 30m Geographic Coverage: Global Frequency of Updates: Annual Date of Content: 2001-2025 Cautions Data are the product of modeling and thus have an inherent degree of error and uncertainty. Users are strongly encouraged to read and fully comprehend the metadata and other available documentation prior to data use. Values are applicable to forest areas only (canopy cover >30 percent and >5 m height or areas with tree cover gain). See Harris et al. (2021) for further information on the forest definition used in the analysis. Although emissions in each pixel are associated with a specific year of disturbance, emissions over an area of interest reflect the total over the model period of 2001-2025. Thus, values must be divided by 25 to calculate average annual emissions. Emissions reflect stand-replacing disturbances as observed in Landsat satellite imagery and do not include emissions from unobserved forest degradation. Emissions reflect a gross estimate, i.e., carbon removals from any regrowth that occurs after disturbance are not included. Instead, gross carbon removals are accounted for in the companion forest carbon removals layer. Emissions data contain temporal inconsistencies. Improvements in the detection of tree cover loss due to the incorporation of new satellite data and methodology changes between 2011 and 2015 may result in higher estimates of emissions in recent years compared to earlier years. Refer here for additional information. Forest carbon emissions do not reflect carbon transfers from ecosystem carbon pools to the harvested wood products (HWP) pool. This dataset has been updated since its original publication. See Overview for more information.本排放图层属于Harris等人（2021）提出的森林碳通量模型（forest carbon flux model）。该论文提出了一套用于估算全球森林碳通量的地理空间监测框架，可助力各类主体与组织追踪森林温室气体通量，并助力减少森林排放或提升森林碳汇。森林碳排放指的是各模拟年份中发生的林分更替型森林干扰所产生的温室气体排放，单位为兆克二氧化碳当量（megagrams CO₂e）/公顷，时间范围为2001年至2025年。 排放涵盖所有相关生态系统碳库：地上生物量、地下生物量、枯木、凋落物、土壤有机碳，以及温室气体（二氧化碳（CO₂）、甲烷（CH₄）、氧化亚氮（N₂O））。针对发生林分更替型干扰的像元（pixel），其排放估算遵循《国家温室气体清单IPCC指南》（IPCC Guidelines for national greenhouse gas inventories），干扰范围参照Hansen等人（2013）发布的《全球森林变化》（Global Forest Change）年度树冠覆盖损失数据。 各像元的碳排放基于2000年的碳密度，并针对2000年至干扰发生年份之间积累的碳进行了调整。本排放为总排放量估算值，即不包含后续森林再生所带来的碳汇。相应地，砍伐后后续再生产生的总碳汇将在配套的森林碳汇图层中进行核算。 干扰发生时各像元的碳排放占比（排放因子）受多个因素影响，包括干扰的直接驱动因子、干扰发生当年或此前是否观测到火灾、干扰是否发生在泥炭地，以及其他更多因素。所有排放均假定发生在干扰发生当年。可通过Hansen树冠覆盖损失数据将排放分配至具体年份，但全球森林观察（Global Forest Watch, GFW）未提供分年度的单独排放栅格数据。 所有输入图层均已重采样至统一的0.00025°×0.00025°分辨率，以匹配Hansen等人（2013）的数据集。本模型自首次发布以来已进行了多次更新。如需查阅当前版本的相关文档，请参阅此博客。如需了解2023年树冠覆盖损失更新（2024年春季发布）中包含的模型修改细节，以及将本模型的通量与《全球碳预算》（Global Carbon Budget）和国家温室气体清单的通量进行对比，请参阅此文章。 可供下载的排放栅格共有三种变体： 1. 2000年树冠覆盖密度（tree cover density, TCD）>30%或存在树冠增益的像元，其排放值为兆克二氧化碳当量/公顷：该数据用于按照全球森林观察默认的树冠覆盖密度阈值可视化（绘制）排放情况，因其代表每公顷的排放密度。若仅希望将排放范围限定在更严格定义的森林像元中，可使用该数据。 2. 2000年树冠覆盖密度>30%或存在树冠增益的像元，其排放值为兆克二氧化碳当量/像元：该数据用于按照GFW默认的树冠覆盖密度阈值计算感兴趣区域（area of interest, AOI）内的排放量，因为可通过对感兴趣区域内各像元的数值求和，得到该区域的总排放量。若仅希望将排放范围限定在更严格定义的森林像元中，可使用该数据。 3. 2000年存在任意程度树冠覆盖或存在树冠增益的像元，其排放值为兆克二氧化碳当量/像元：该数据用于在不设置树冠覆盖密度阈值的情况下计算感兴趣区域内的排放量，因为可通过对感兴趣区域内各像元的数值求和，得到该区域的总排放量。该数据代表未施加树冠覆盖密度阈值的感兴趣区域内树冠覆盖损失产生的总排放量。若希望将2000年树冠覆盖密度较低（<30%）的像元纳入排放范围，可使用该数据。 兆克二氧化碳当量/像元图层中的数值，是通过将单位公顷排放量按照各像元的面积进行调整后得到的，而像元面积随纬度变化。2000年的树冠覆盖密度数据参照Hansen等人（2013）的研究，2000年至2020年的树冠增益数据参照Potapov等人（2022）的研究。 相关开放数据门户图层：森林碳汇、森林净碳通量 Google Earth Engine：资产（2000年树冠覆盖密度>30%的像元的兆克二氧化碳当量/公顷排放量）与可视化脚本 分辨率：30×30米 地理覆盖范围：全球 更新频率：年度 数据内容时间范围：2001-2025年 注意事项 本数据为建模产物，因此存在固有的误差与不确定性。强烈建议用户在使用数据前，仔细阅读并充分理解元数据及其他可用文档。 本数据仅适用于森林区域（树冠覆盖率>30%且高度>5米，或存在树冠增益的区域）。有关本分析中使用的森林定义的更多信息，请参阅Harris等人（2021）的论文。 尽管每个像元的排放均对应具体的干扰年份，但感兴趣区域内的排放总量为2001-2025年整个模拟周期内的总和。因此，若要计算年均排放量，需将总数值除以25。 本排放仅反映Landsat卫星影像中观测到的林分更替型干扰，不包含未被观测到的森林退化所产生的排放。本排放为总排放量估算值，即不包含干扰发生后任何再生森林所带来的碳汇。相应地，总碳汇将在配套的森林碳汇图层中进行核算。 本排放数据存在时间不一致性问题。2011年至2015年间，由于纳入了新的卫星数据并改进了方法，树冠覆盖损失的检测精度有所提升，这可能导致近年的排放估算值高于早年。如需了解更多信息，请参阅此处。 森林碳排放不包含从生态系统碳库转移至采伐林产品（harvested wood products, HWP）库的碳。本数据集自首次发布以来已进行多次更新。更多信息请参阅本概述部分。