Decadal decrease in Los Angeles methane emissions is much smaller than bottom-up estimates

Creators: Zeng, Zhao-Cheng¹; Pongetti, Thomas²; Newman, Sally¹; Oda, Tomohiro; Gurney, Kevin; Palmer, Paul I.; Yung, Yuk L.¹; Sander, Stanley P.¹

1. California Institute of Technology
2. Jet Propulsion Lab

Abstract

Methane, a powerful greenhouse gas, has a short atmospheric lifetime ( ~ 12 years), so that emissions reductions will have a rapid impact on climate forcing. In megacities such as Los Angeles (LA), natural gas (NG) leakage is the primary atmospheric methane source. The magnitudes and trends of fugitive NG emissions are largely unknown and need to be quantified to verify compliance with emission reduction targets. Here we use atmospheric remote sensing data to show that, in contrast to the observed global increase in methane emissions, LA area emissions decreased during 2011-2020 at a mean rate of (–1.57 ± 0.41) %/yr. However, the NG utility calculations indicate a much larger negative emissions trend of −5.8 %/yr. The large difference between top-down and bottom-up trends reflects the uncertainties in estimating the achieved emissions reductions. Actions taken in LA can be a blueprint for COP28 and future efforts to reduce methane emissions.

Copyright and License

© The Author(s) 2023. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Acknowledgement

Flask data provided by Dr. Ed Dlugokencky and Dr. Arlyn Andrews (NOAA) are greatly appreciated. Comments from K.-F. Li and J. Pinto are gratefully acknowledged. Funding is acknowledged from NASA grant 80NSSC21K1929 (T.O.) and NIST grant 70NANB19H129 (K. G.) P.I.P. acknowledges support from the UK National Centre for Earth Observation (NCEO) funded by the Natural Environment Research Council (NE/R016518/1). S.S. and T.P. acknowledge support for the CLARS facility from the NASA Earth Science Directorate and the JPL Earth Science and Technology Directorate. The research was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

Contributions

S.S. and Z.-C.Z designed the study. Z.-C. Z., T.P., S.S. and S.N. carried out the experiments. S.S., Z.-C.Z., P.P., Y.L.Y. and S.N. analyzed the results. T.O. and K.G. provided carbon dioxide emission inventories. Z.-C.Z. and S.S. wrote the paper. All authors reviewed the manuscript.

Data Availability

CLARS-FTS XCO₂ and XCH₄ data are publicly available at https://data.caltech.edu/records/254mc-zpg74 (10.22002/D1.1985). NOAA carbon cycle surface flask measurements on Mt. Wilson are available from https://gml.noaa.gov/dv/site/site.php?code=MWO and can be requested from NOAA Earth System Research Laboratories. Bottom up inventory of CO₂ emissions from ODIAC are publicly available from https://db.cger.nies.go.jp/dataset/ODIAC/, from California Air Resources Board are available from https://ww2.arb.ca.gov/ghg-inventory-data, and from Hestia v2.5 are publicly available from https://hestia.rc.nau.edu/; The reports of quarterly natural gas usage are publicly available from SoCalGas at https://www.socalgas.com/for-your-business/energy-savings/energy-usage-requests.

Code Availability

The EEMD codes (in Matlab) used to determine the CH₄ emissions trends are located in the CaltechData repository at 10.22002/5f3rd-xqr42.

Conflict of Interest

The authors declare no competing interests.

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