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Net forest greenhouse gas flux 2001-2022

Net forest greenhouse gas flux 2001-2022

Posted on June 27, 2023
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What’s New With GFW’s Forest Carbon Monitoring

Posted on June 27, 2023
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GFW newsletter

The Intergovernmental Panel on Climate Change’s (IPCC) latest Assessment Report reminds us that forests play a crucial role in the global carbon cycle and mitigating climate change. To act on that report and manage and protect forests — from policies to on-the-ground action — governments, companies, Indigenous Peoples and civil society need information on where forests are gaining or losing carbon.

To support these groups and others, Global Forest Watch (GFW) released maps and associated statistics of forest greenhouse gas emissions, sequestration (forest carbon removals) and net greenhouse gas flux (the difference between them) in 2021 based on a geospatial framework designed to be improved over time as relevant new data and information are produced. Since the framework’s original publication, we have updated it and associated maps and data available on GFW as each new year of tree cover loss data is released.

In 2023, in addition to the standard update of tree cover loss data and drivers of tree cover loss for 2022, we made additional improvements to the inputs to the framework using other recently available geospatial data. Read on to learn about what’s new and what’s next for GFW’s global forest carbon monitoring.

What is GFW’s forest carbon flux monitoring framework and how has it been used?

GFW’s geospatial forest carbon flux monitoring framework is based on the land use, land-use change and forestry part of the Agriculture, Forestry and Other Land Use (AFOLU) guidelines developed by the IPCC, which all national governments use for their greenhouse gas inventory reporting. However, rather than relying on statistical data on forests like most national governments do, the framework takes a geospatial approach by combining multiple relevant Earth observation data sets to derive estimates about how each 30×30-meter piece of forest has contributed to global carbon emissions and removals from 2001 onwards. Read more about the framework and how it was developed here.

The carbon flux data, showing emissions, removals and net flux, is available on the GFW map and is updated annually 

Many actors and organizations have used GFW’s forest carbon data to monitor carbon fluxes, for example, in UNESCO World Heritage sites, in forests managed by Indigenous Peoples, throughout the Amazon, by companies for their greenhouse gas inventories, for tracking global commitments, in the IPCC Sixth Assessment Report, in scientific research and more.

Updates to the forest carbon flux monitoring framework in 2023

We designed the forest carbon monitoring framework to be flexible enough to incorporate scientific and technical advances in geospatial data to ensure that it continues to be based on the best available data. This year, we updated several of the data sources used in the framework. Some of these address limitations in the original analysis, while others bring the framework in line with recent scientific advances.

Along with our annual updates to tree cover loss and the drivers  of tree cover loss, there are five additional updates:

1. Locally variable root biomass. The framework uses a global 30-m aboveground woody biomass map for the year 2000 as the basis for biomass in tree roots (belowground biomass), and both are used as the starting point for mapping emissions and removals from 2001 onwards. The framework originally assumed that belowground biomass was 26% of aboveground biomass (also known as the root-shoot ratio) for all forests outside of mangroves,* regardless of forest type or climate. However, the root-shoot ratio can vary significantly depending on forest type and climate.

With the 2023 update, the framework now uses a wall-to-wall map of the ratio of belowground to aboveground biomass, with values that range from less than 15% to more than 150%. This update improves local estimation of belowground biomass and thus carbon emissions and removals. While using this new root-shoot ratio map should not substantially impact global estimates, the update will improve local estimation of belowground biomass in places where the root-shoot ratio is significantly different from the global average.

2. Updated tree cover gain through 2020. While the original framework only included tree cover gain between 2000 and 2012, it now includes tree cover gain through 2020 based on data launched on GFW last year. This improves emissions and removals estimates because tree cover gain is now monitored over nearly the entire period of analysis. Although tree cover gain since 2020 is not captured by the framework — nor is information on the individual years in which tree cover gain occurred — up-to-date, annualized tree cover gain data is under development and will be incorporated into the framework when it becomes available.

3. Higher resolution forest fire data. The framework originally attributed tree cover loss due to fires using a 500-m MODIS burned area product. In the 2023 update, we replaced this with 30-m data on tree cover loss due to fires from the University of Maryland (UMD), designed to be used in conjunction with and at the same spatial resolution as the annual tree cover loss data. We made this change because, unlike the MODIS burned area product, the new data from UMD is specifically trained to detect fire-related tree cover loss. This difference, combined with the higher spatial resolution of the tree cover loss due to fire data, captures fire activity more precisely and, therefore, improves our estimates of carbon emissions associated with forest fires. Globally, the new 30-m fire data set attributes about 20% more tree cover loss to fires than the 500-m MODIS product.

4. Updated peat extent. We improved the global peat map used in the framework by incorporating recently published regional maps. These increased peat extent in the Congo Basin and lowland Peruvian Amazon and should more accurately reflect the extent of emissions from peat drainage where relevant.

5. Updated Global Warming Potential values. Global Warming Potential (GWP) values are used to convert emissions of non-CO2 gases like methane and nitrous oxide into equivalent units of carbon dioxide so that the global warming impacts of different greenhouse gases can be compared and added together into a single value in units of CO2 equivalents. In the original framework, GWP values were taken from the IPCC Fifth Assessment Report (AR5). It now uses updated GWP values from the IPCC Sixth Assessment Report (AR6). This change only affects emissions of non-CO2 gases, which occur in areas of forest fire and peat drainage.

Framework  update

Previous version

Current version

Affects emissions

Affects removals

Source for belowground carbon

Used global ratio of 0.26 for belowground carbon to aboveground carbon for non-mangrove forests.

Uses Huang et al. 2021 map of ratio of belowground carbon to aboveground carbon for non-mangrove forests. This ratio map was extended outwards to fill gaps in the original map.



Years of tree cover gain

Covered 2000-2012, from Hansen et al. 2013

Covers 2000-2020, from Potapov et al. 2022



Source for fire data

MODIS burned area, from Giglio et al. 2018

UMD’s tree cover loss from fires, from Tyukavina et al. 2022



Sources for peat map



Source for Global Warming Potential (GWP) values

From the IPCC Fifth Assessment Report, Table 8.7. GWP-100 is 28 for methane and 265 for nitrous oxide (no climate-carbon feedback).

From the IPCC Sixth Assessment Report, Table 7.15. GWP-100 is 27 for methane (non-fossil) and 273 for nitrous oxide.



What’s next for the forest carbon flux framework?

GFW is moving towards monitoring forest extent and change with height-based measurement of forests, and our carbon monitoring framework is following suit. Forthcoming annual maps of forest extent, loss and gain based on changes in canopy height will contribute to more detailed timeseries of forest carbon emissions and removals.

GFW is also collaborating with partners to develop new, data-driven methods to improve the spatial and temporal distribution of forest carbon sequestration rates in the world’s standing forests using a few different approaches. These will improve one of the coarsest parts of the current framework.

Finally, the forest flux framework will be integrated into a broader Agriculture, Forestry and Other Land Uses (AFOLU) greenhouse gas flux framework in 2024. This will expand greenhouse gas monitoring from forests to all land uses (such as grasslands), as well as incorporate the “A” (agriculture) of AFOLU by mapping emissions from agricultural activities such as drained cropland soils, fertilizer application and rice cultivation, as well as emissions from the world’s livestock systems.

In the two years since its release, GFW’s forest carbon flux monitoring framework has already been used in a variety of science and policy applications to make local, data-driven decision making around forest carbon possible. The recent improvements, and bigger updates on the horizon, use the best available data to help the global community monitor, assess and prioritize action to reduce emissions from deforestation, increase carbon sequestration from forest restoration and protect and enhance the global forest carbon sink.

* Mangrove forests store proportionately more biomass in their root systems than other forest types; this is reflected in the framework.

We are continuously working to improve GFW data sets, and feedback from users can help us understand current gaps in forest carbon monitoring and decide what improvements to make next. If you have used any of GFW’s carbon data, please tell us about it.

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