Global Methane Budget 2000-2020: Progress and Remaining Challenges

Atmospheric methane is the second most important anthropogenic greenhouse gas after carbon dioxide. With a lifetime around 10 years in the atmosphere and a wide diversity of anthropogenic and natural emission types, methane is a complex GHG to track and a key climate change leaver. Observations of atmospheric methane began in 1978, and now include a large variety of in-situ and remote-sensed observations from the surface and space. These data are assimilated in atmospheric inversion to infer methane emissions and sinks (top-down approaches). In parallel, a large international effort has been conducted to model processes emitting methane at the surface (e.g. wetland emissions) and destroying methane in the atmosphere (e.g. OH radicals), while the compilation of inventories of anthropogenic emissions has increased in complexity and refinement (bottom-up approaches).

However, large uncertainties remain in the spatio-temporal quantification of methane sources and sinks. The Global Carbon Project-Methane aims to establish a synthesis of the global methane budget with regularly updated releases. We will present the results and main outcomes from the latest soon-to-be-released (Saunois et al., 2024, submitted) covering 2000-2020. We will discuss the improvements over previous releases, including reduced double counting for inland waters emissions, and a more comprehensive assessment of coastal emissions. Remaining uncertainties and next priorities include the integration of higher resolution distribution of inland waters in atmospheric inversion models, improved atmospheric transport and chemistry models to integrate robust representation of OH fields in atmospheric models,overlay satellite-based estimates on likely underestimated industrial super-emitters, and integration of other regional higher resolution assessments.

References

Saunois M, Martinez A., Poulter B, Zhang Z, Raymond P A, Regnier P,  Canadell J P,  Jackson R B , Patra P K, Bousquet P,  Ciais P, Dlugokencky E J, Lan X et al. (2024) Global Methane Budget 2000-2020. ESSD, submitted.