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 similar to-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. East Asia (China, Japan, Koreas and Mongolia) is not only the hotspot of anthropogenic greenhouse gas (GHG, including CO2, CH4 and N2O) emissions, but also a region with large CO2 sink. However, the greenhouse gas balance of greenhouse gases over the region is poorly understood. In this study, we performed a synthesis for over 40 flux terms to provide the first-of-its-kind GHG budget assessment over the decades of 2000s and 2010s. We find terrestrial ecosystems in East Asia is close to neutrality of GHGs. The bottom-up approach summing up component fluxes estimated a net balance of -36.1 +/- 207.1 Tg CO2eq yr-1, while the top-down approach based on atmospheric inversions estimated a net balance of -46.3 +/- 505.9 Tg CO2eq yr-1. This results from compensation of the large CO2 sink by CH4 and N2O emissions, and from compensation of net GHG sink over natural ecosystems by net GHG source over agricultural ecosystems. Thus, curbing agricultural GHG emissions has the potential to realizing the ambitious goal of achieving climate neutrality over East Asia. A comprehensive greenhouse gas (CO2, CH4 and N2O) accounting including about 40 flux terms over East Asia is reported Terrestrial ecosystems in East Asia are close to greenhouse gas neutral Natural ecosystems is a net greenhouse gas sink, compensated by a net source from agricultural ecosystems