A 30-Year Record of  the Isotopic Composition of Atmospheric Methane

Teama, D. G.

doi:10.15760/etd.642

Cited by 2 publications

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“…S1). Measurements of δ 13 C and δD of CH 4 were made by continuous-flow gas chromatography isotope ratio mass-spectrometry on a Thermo Scientific Delta V IRMS as described previously (34,35) (SI Appendix, section S.1). [Note, by convention, isotope ratios are expressed using the delta notation (as δ values), where Inverse Modeling.…”

Section: Methodsmentioning

confidence: 99%

Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase

Rice

Butenhoff

Teama

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

114

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Observations of atmospheric methane (CH 4 ) since the late 1970s and measurements of CH 4 trapped in ice and snow reveal a meteoric rise in concentration during much of the twentieth century. Since 1750, levels of atmospheric CH 4 have more than doubled to current globally averaged concentration near 1,800 ppb. During the late 1980s and 1990s, the CH 4 growth rate slowed substantially and was near or at zero between 1999 and 2006. There is no scientific consensus on the drivers of this slowdown. Here, we report measurements of the stable isotopic composition of atmospheric CH 4 ( 13 C/ 12 C and D/H) from a rare air archive dating from 1977 to 1998. Together with more modern records of isotopic atmospheric CH 4 , we performed a time-dependent retrieval of methane fluxes spanning 25 y (1984-2009) using a 3D chemical transport model. This inversion results in a 24 [18,27] Tg y −1 CH 4 increase in fugitive fossil fuel emissions since 1984 with most of this growth occurring after year 2000. This result is consistent with some bottom-up emissions inventories but not with recent estimates based on atmospheric ethane. In fact, when forced with decreasing emissions from fossil fuel sources our inversion estimates unreasonably high emissions in other sources. Further, the inversion estimates a decrease in biomass-burning emissions that could explain falling ethane abundance. A range of sensitivity tests suggests that these results are robust.atmospheric methane | greenhouse gas emissions | methane isotopic composition | methane trends | Bayesian inversion C onsiderable research since the 1970s has established the role of methane (CH 4 ) in climate, as an infrared active gas, and as a chemically reactive species affecting hydroxyl radical, ozone, and carbon monoxide in the troposphere and chlorine, ozone, and water vapor in the stratosphere. At a globally averaged mixing ratio of 1,800 ppb, the abundance of CH 4 in the atmosphere has more than doubled since the industrial revolution as a result of population growth, agricultural practices, and fossil fuel use (1). The rise in CH 4 concentration is considered to contribute 0.48 Wm −2 of the 2.83 Wm −2 radiative forcing by wellmixed greenhouse gases since 1750 (2). Including indirect effects from CH 4 emissions roughly doubles its effective radiative forcing. Its global warming potential (not including feedbacks) is 28 based on a 100-y time horizon, but 84 based on a 20-y timescale [global warming potential (GWP) is relative to CO 2 ], illustrating the potential of large changes in the burden of CH 4 to influence climate on short timescales (2).Both the decrease in the CH 4 growth rate and its interannual variability since 1984 are well documented by at least four global networks of atmospheric measurements; agreement between time series is excellent with some exceptions early on. Recently, a review and synthesis of the CH 4 budget (3) pointed to some consensus of measurement and modeling studies and their comparisons toward understanding temporal changes in the CH 4 budget....

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Section: Methodsmentioning

confidence: 99%

Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase

Rice

Butenhoff

Teama

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

114

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“…The PDX measurement system has been described in Teama (2013) with some updates since Rice et al (2001). The δ 13 C-CH 4 and δD-CH 4 reproducibilities are 0.07 and 2.0 ‰, respectively, and PDX shares the standard scales with UCI for both δ 13 C-CH 4 and δD-CH 4 (Rice et al, 2016).…”

Section: Pdxmentioning

confidence: 99%

“…Since PDX follows the UCI standard scale (Teama, 2013;Rice et al, 2016), the likely offset is the same as that of UCI (no. 12 in Fig.…”

Section: δD-chmentioning

confidence: 99%

Interlaboratory comparison of δ13C and δD measurements of atmospheric CH4 for combined use of data sets from different laboratories

et al. 2018

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Abstract. We report results from a worldwide interlaboratory comparison of samples among laboratories that measure (or measured) stable carbon and hydrogen isotope ratios of atmospheric CH 4 (δ 13 C-CH 4 and δD-CH 4 ). The offsets among the laboratories are larger than the measurement reproducibility of individual laboratories. To disentangle plausible measurement offsets, we evaluated and critically assessed a large number of intercomparison results, some of which have been documented previously in the literature. The results indicate significant offsets of δ 13 C-CH 4 and δD-CH 4 measurements among data sets reported from different laboratories; the differences among laboratories at modern atmospheric CH 4 level spread over ranges of 0.5 ‰ for δ 13 C-CH 4 and 13 ‰ for δD-CH 4 . The intercomparison results summarized in this study may be of help in future attempts to harmonize δ 13 C-CH 4 and δD-CH 4 data sets fromPublished by Copernicus Publications on behalf of the European Geosciences Union. 1208T. Umezawa et al.: Interlaboratory comparison of δ 13 C and δD measurements of CH 4 different laboratories in order to jointly incorporate them into modelling studies. However, establishing a merged data set, which includes δ 13 C-CH 4 and δD-CH 4 data from multiple laboratories with desirable compatibility, is still challenging due to differences among laboratories in instrument settings, correction methods, traceability to reference materials and long-term data management. Further efforts are needed to identify causes of the interlaboratory measurement offsets and to decrease those to move towards the best use of available δ 13 C-CH 4 and δD-CH 4 data sets.

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A 30-Year Record of the Isotopic Composition of Atmospheric Methane

Cited by 2 publications

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Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase

Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase

Interlaboratory comparison of <i>δ</i><sup>13</sup>C and <i>δ</i>D measurements of atmospheric CH<sub>4</sub> for combined use of data sets from different laboratories

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A 30-Year Record of the Isotopic Composition of Atmospheric Methane

Cited by 2 publications

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Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase

Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increase

Interlaboratory comparison of &lt;i&gt;δ&lt;/i&gt;&lt;sup&gt;13&lt;/sup&gt;C and &lt;i&gt;δ&lt;/i&gt;D measurements of atmospheric CH&lt;sub&gt;4&lt;/sub&gt; for combined use of data sets from different laboratories

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Interlaboratory comparison of <i>δ</i><sup>13</sup>C and <i>δ</i>D measurements of atmospheric CH<sub>4</sub> for combined use of data sets from different laboratories