The Global Methane Budget: 2000–2012

Abstract

Abstract. The global methane (CH4) budget is becoming an increasingly important component for managing realistic pathways to mitigate climate change. This relevance, due to a shorter atmospheric lifetime and a stronger warming potential than carbon dioxide, is challenged by the still unexplained changes of atmospheric CH4 over the past decade. Emissions and concentrations of CH4 are continuing to increase making CH4 the second most important human-induced greenhouse gas after carbon dioxide. Two major difficulties in reducing uncertainties come from the large variety of diffusive CH4 sources that overlap geographically, and from the destruction of CH4 by the very short-lived hydroxyl radical (OH). To address these difficulties, we have established a consortium of multi-disciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate research on the methane cycle, and producing regular (~biennial) updates of the global methane budget. This consortium includes atmospheric physicists and chemists, biogeochemists of surface and marine emissions, and socio-economists who study anthropogenic emissions. Following Kirschke et al. (2013), we propose here the first version of a living review paper that integrates results of top-down studies (T-D, exploiting atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up models, inventories, and data-driven approaches (B-U, including process-based models for estimating land surface emissions and atmospheric chemistry, and inventories for anthropogenic emissions, data-driven extrapolations). For the 2003–2012 decade, global methane emissions are estimated by T-D inversions at 558 Tg CH4 yr−1 (range [540–568]). About 60 % of global emissions are anthropogenic (range [50–65 %]). B-U approaches suggest larger global emissions (736 Tg CH4 yr−1 [596–884]) mostly because of larger natural emissions from individual sources such as inland waters, natural wetlands and geological sources. Considering the atmospheric constraints on the T-D budget, it is likely that some of the individual emissions reported by the B-U approaches are overestimated, leading to too large global emissions. Latitudinal data from T-D emissions indicate a predominance of tropical emissions (~64 % of the global budget,

U.S. CH4 emissions from oil and gas production: Have recent large increases been detected?

“…Atmospheric inversions combine atmospheric mole fraction observations, emissions from inventories and process-based models ("priors"), and atmospheric chemistry-transport models to infer spatially and temporally resolved optimized ("posterior") methane emissions and their uncertainties. The Global Carbon Project gathered 30 different global inversions provided by 8 different research groups worldwide for 2000-2012 (Saunois et al [2016], updating Kirschke et al [2013]). The different inversions (see Table 1) vary in the observations assimilated (e.g., surface observations and/or retrievals of column average CH 4 from GOSAT or Scanning Imaging Absorption Spectrometer for Atmospheric Chartography, on Envisat (SCIAMACHY) spaceborne instruments), the atmospheric chemical transport model used, and the inversion set up (prior emissions, prior uncertainties, and inverse technique).…”

Quantifying the loss of processed natural gas within California's South Coast Air Basin using long-term measurements of ethane and methane

“…Anthropogenic sources of the potent greenhouse gas methane (CH 4 ) constitute about 60 % of the global total CH 4 emissions, or nearly 350 Tg CH 4 yr −1 (Saunois et al, 2016). Urban regions are thought to be an important contributor to this flux (e.g., McKain et al, 2012), and thus both quantification and attribution of these urban sources are crucial for fully understanding their causes and hence potentially regulating them.…”

Assessment of Anthropogenic Methane Emissions over Large Regions Based on GOSAT Observations and High Resolution Transport Modeling

“…Methane is released to the atmosphere by both natural and anthropogenic sources, and is depleted by oxidation with hydroxyl radical (OH) in the troposphere, oxidation with drier soil and by photolysis in the stratosphere. Anthropogenic emission contributes approximately 50-65% of the global methane budget [2]. Due to the large radiative forcing, reducing anthropogenic CH 4 emission is important for mitigation of potential impact of global warming (e.g., [3]).…”

“…Due to the large radiative forcing, reducing anthropogenic CH 4 emission is important for mitigation of potential impact of global warming (e.g., [3]). The atmospheric CH 4 level has drastically increased since the industrial revolution [4], and its growth rate exhibits large interannual variability over recent few decades [5], the causes of which are not fully understood on a global scale (e.g., [2,5,6]). In addition, in the context of recent slowdown in global warming, atmospheric methane variability and the anthropogenic contribution to this variability is particularly important [7,8].…”