Revised and updated geospatial monitoring of 21st century forest carbon fluxes

Abstract

Earth observation data are increasingly used to estimate the magnitude and geographic distribution of greenhouse gas (GHG) fluxes and reduce overall uncertainty in the global carbon budget, including for forests. Here, we report on a revised and updated geospatial, Earth-observation-based modeling framework that maps GHG emissions, carbon removals, and the net balance between them globally for forests from 2001 to 2023 at roughly 30 m resolution, hereafter referred to as the Global Forest Watch (GFW) model (see the “Code and data availability” section). Revisions address some of the original model's limitations, improve model inputs, and refine the uncertainty analysis. We found that, between 2001 and 2023, global forest ecosystems were, on average, a net sink of −5.5 ± 8.1 Gt CO2e yr−1 (gigatonnes of CO2 equivalent per year ± 1 standard deviation), which reflects the balance of 9.0 ± 2.7 Gt CO2e yr−1 of GHG emissions and −14.5 ± 7.7 Gt CO2 yr−1 of removals, with an additional −0.20 Gt CO2 yr−1 transferred into harvested wood products. Uncertainty in gross removals was greatly reduced compared with the original model due to the refinement of uncertainty for carbon removal factors in temperate secondary forests. After reallocating GFW's gross CO2 fluxes into anthropogenic fluxes from forest land and deforestation categories to increase the conceptual similarity with national greenhouse gas inventories (NGHGIs), we estimated a global net anthropogenic forest sink of −3.6 Gt CO2 yr−1, excluding harvested wood products, with the remaining net CO2 flux of −2.2 Gt CO2 yr−1 reported by the GFW model as non-anthropogenic. Although the magnitude of GFW's translated estimates aligns relatively well with aggregated NGHGIs, the temporal trends differ. Translating Earth-observation-based flux estimates into the same reporting framework that countries use for NGHGIs helps build confidence around land use carbon fluxes and supports independent evaluation of progress towards Paris Agreement goals. The data availability is as follows: carbon removals (Gibbs et al., 2024a, https://doi.org/10.7910/DVN/V2ISRH), GHG emissions (Gibbs et al., 2024b, https://doi.org/10.7910/DVN/LNPSGP), and net flux (Gibbs et al., 2024c, https://doi.org/10.7910/DVN/TVZVBI).