The Greenhouse Gas Budget of Terrestrial Ecosystems in East Asia Since 2000

East Asia (China, Japan, Koreas, and Mongolia) has been the world's economic engine over at least the past two decades, exhibiting a rapid increase in fossil fuel emissions of greenhouse gases (GHGs) and has expressed the recent ambition to achieve climate neutrality by mid-century. However, the GHG balance of its terrestrial ecosystems remains poorly constrained. Here, we present a synthesis of the three most important long-lived greenhouse gases (CO₂, CH₄, and N₂O) budgets over East Asia during the decades of 2000s and 2010s, following a dual constraint approach. We estimate that terrestrial ecosystems in East Asia is close to neutrality of GHGs, with a magnitude of between −46.3 ± 505.9 Tg CO₂eq yr⁻¹ (the top-down approach) and −36.1 ± 207.1 Tg CO₂eq yr⁻¹ (the bottom-up approach) during 2000–2019. This net GHG sink includes a large land CO₂ sink (−1229.3 ± 430.9 Tg CO₂ yr⁻¹ based on the top-down approach and −1353.8 ± 158.5 Tg CO₂ yr⁻¹ based on the bottom-up approach) being offset by biogenic CH₄ and N₂O emissions, predominantly coming from the agricultural sectors. Emerging data sources and modeling capacities have helped achieve agreement between the top-down and bottom-up approaches, but sizable uncertainties remain in several flux terms. For example, the reported CO₂ flux from land use and land cover change varies from a net source of more than 300 Tg CO₂ yr⁻¹ to a net sink of ∼−700 Tg CO₂ yr⁻¹. Although terrestrial ecosystems over East Asia is close to GHG neutral currently, curbing agricultural GHG emissions and additional afforestation and forest managements have the potential to transform the terrestrial ecosystems into a net GHG sink, which would help in realizing East Asian countries' ambitions to achieve climate neutrality.