The Greenhouse Gas Budget of Southeast Asia for 2000-2019 and Pathways Toward Climate Neutrality

Member countries of the Association of Southeast Asian Nations ratified the Paris Agreement and have initiated their own efforts to reduce greenhouse gas (GHG) emissions. However, the progress of these countries toward climate neutrality remains uncertain. Here, we estimated the combined budget for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in Southeast Asia for 2000-2019 using bottom-up and top-down approaches. The CO2 emissions from deforestation were the largest source, followed by anthropogenic fire emissions, which together exceeded the CO2 uptake by natural vegetation and land-use change legacy (e.g., regrowth), yielding a net source of CO2 in the biosphere. The region's biosphere was also a net source of CH4 and N2O, which, combined with the CO2 budget, makes the Southeast Asian biosphere a net source of GHGs to the atmosphere, ranging from 2,003.2 +/- 406.1 Tg CO2eq yr-1 (bottom-up) to 2,227.5 +/- 572.8 Tg CO2eq yr-1 (top-down) for 2000-2019. Among non-biospheric GHG emissions (e.g., fossil fuels and waste-related emissions), coal usage has resulted in an unprecedented increase in CO2 emissions. The total GHG budget (the biospheric GHG budget plus the non-biospheric GHG fluxes) was calculated as a net source of 3,226.3 +/- 406.2 Tg CO2eq yr-1 (bottom-up) and 3,406.4 +/- 572.9 Tg CO2eq yr-1 (top-down) for 2000-2019. Our study revealed that Southeast Asia is experiencing the dual challenge of large emissions from deforestation and coal usage, necessitating the implementation of urgent mitigation strategies to ensure climate neutrality.