Methane emissions from Australia estimated by inverse analysis using in-situ and Satellite (GOSAT) atmospheric observations

Australia has significant sources of atmospheric methane (CH₄), driven by extensive coal and natural gas production, livestock, and large-scale fires. Accurate quantification and characterization of CH₄ emissions are critical for effective climate mitigation strategies in Australia. In this study, we employed an inverse analysis of atmospheric CH₄ observations from the GOSAT satellite and surface measurements from 2016 to 2021 to assess CH₄ emissions in Australia. The inversion process integrates anthropogenic and natural emissions as prior estimates, optimizing them with the NIES-TM-FLEXPART-variational model (NTFVAR) at a resolution of up to 0.1° × 0.1°. We validated the performance of our inverse model using data obtained from the United Nations Environment Program Methane Science (UNEP), Airborne Research Australia 2018 aircraft-based atmospheric CH₄ measurement campaigns. Compared to prior emission estimates, optimized emissions dramatically enhanced the accuracy of modeled concentrations, aligning them much better with observations. Our results indicate that the estimated inland CH₄ emissions in Australia amount to 6.84 ± 0.51 Tg CH₄ yr⁻¹ and anthropogenic emissions amount to 4.20 ± 0.08 Tg CH₄ yr⁻¹, both slightly lower than the values reported in existing inventories. Moreover, our results unveil noteworthy spatiotemporal characteristics, such as upward corrections during the warm season, particularly in Southeastern Australia. During the three most severe months of the 2019–2020 bushfire season, emissions from biomass burning surged by 0.68 Tg, constituting over 71% of the total emission increase. These results highlight the importance of continuous observation and analysis of sectoral emissions, particularly near major sources, to guide targeted emission reduction strategies. The spatiotemporal characteristics identified in this study underscore the need for adaptive and region-specific approaches to CH₄ emission management in Australia.

澳大利亚拥有丰富的大气甲烷（CH₄）排放源，其排放主要由大规模煤炭与天然气生产、畜牧业活动以及大范围野火驱动。准确量化并表征甲烷排放，对于澳大利亚制定高效的气候减缓策略至关重要。本研究采用2016—2021年温室气体观测卫星（GOSAT）的大气甲烷观测数据与地面观测资料开展反演分析，以评估澳大利亚境内的甲烷排放。反演流程整合了人为与自然排放的先验估算值，并借助分辨率最高达0.1°×0.1°的NIES-TM-FLEXPART变分模型（NTFVAR）对其进行优化。本研究借助联合国环境规划署甲烷科学计划（UNEP）与2018年澳大利亚机载大气甲烷观测航次获取的数据，对反演模型的性能进行了验证。相较于先验排放估算值，优化后的排放结果显著提升了模拟浓度的准确性，使模拟结果与观测数据的匹配度大幅提升。本研究估算的澳大利亚内陆甲烷排放总量为6.84±0.51太克甲烷每年（Tg CH₄ yr⁻¹），人为排放总量为4.20±0.08 Tg CH₄ yr⁻¹，两项数值均略低于现有排放清单的报道值。此外，本研究还揭示了显著的时空分布特征：例如暖季（尤其是澳大利亚东南部）的排放需向上修正。在2019—2020年林火季最严重的三个月中，生物质燃烧排放激增0.68太克，占总排放量增量的71%以上。上述研究结果凸显了持续开展分部门排放观测与分析的重要性，尤其是在主要排放源附近，以指导针对性的减排策略制定。本研究识别的时空分布特征，也表明澳大利亚甲烷排放管理需采用因地制宜的自适应方案。