Societal shifts due to COVID-19 reveal large-scale complexities and feedbacks between atmospheric chemistry and climate change

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Significance

The COVID-19 pandemic and associated lockdowns caused significant changes to human activity that temporarily altered our imprint on the atmosphere, providing a brief glimpse of potential future changes in atmospheric composition. This event demonstrated key feedbacks within and between air quality and the carbon cycle: Improvements in air quality increased the lifetime of methane (an important greenhouse gas), while unusually hot weather and intense wildfires in Los Angeles drove poor air quality. This shows that efforts to reduce greenhouse gas emissions and improve air quality cannot be considered separately.

Abstract

The COVID-19 global pandemic and associated government lockdowns dramatically altered human activity, providing a window into how changes in individual behavior, enacted en masse, impact atmospheric composition. The resulting reductions in anthropogenic activity represent an unprecedented event that yields a glimpse into a future where emissions to the atmosphere are reduced. Furthermore, the abrupt reduction in emissions during the lockdown periods led to clearly observable changes in atmospheric composition, which provide direct insight into feedbacks between the Earth system and human activity. While air pollutants and greenhouse gases share many common anthropogenic sources, there is a sharp difference in the response of their atmospheric concentrations to COVID-19 emissions changes, due in large part to their different lifetimes. Here, we discuss several key takeaways from modeling and observational studies. First, despite dramatic declines in mobility and associated vehicular emissions, the atmospheric growth rates of greenhouse gases were not slowed, in part due to decreased ocean uptake of CO ₂ and a likely increase in CH ₄ lifetime from reduced NO _x emissions. Second, the response of O ₃ to decreased NO _x emissions showed significant spatial and temporal variability, due to differing chemical regimes around the world. Finally, the overall response of atmospheric composition to emissions changes is heavily modulated by factors including carbon-cycle feedbacks to CH ₄ and CO ₂, background pollutant levels, the timing and location of emissions changes, and climate feedbacks on air quality, such as wildfires and the ozone climate penalty.

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Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement

Corinne Le Quéré, Robert B. Jackson, Matthew Jones … (2020)

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Evolution of organic aerosols in the atmosphere.

J. L. Jimenez, M. R. Canagaratna, N. M. Donahue … (2009)

Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high-time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.

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Is Open Access

The Global Methane Budget 2000–2017

Marielle Saunois, Ann Stavert, Ben Poulter … (2020)

Abstract. Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or 50 %–65 %). The mean annual total emission for the new decade (2008–2017) is 29 Tg CH4 yr−1 larger than our estimate for the previous decade (2000–2009), and 24 Tg CH4 yr−1 larger than the one reported in the previous budget for 2003–2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr−1, range 594–881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (∼ 65 % of the global budget, < 30∘ N) compared to mid-latitudes (∼ 30 %, 30–60∘ N) and high northern latitudes (∼ 4 %, 60–90∘ N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters. Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH4 yr−1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH4 yr−1 by 8 Tg CH4 yr−1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning. The data presented here can be downloaded from https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.

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Author and article information

Journal

Journal ID (nlm-ta): Proc Natl Acad Sci U S A

Journal ID (iso-abbrev): Proc Natl Acad Sci U S A

Journal ID (hwp): pnas

Journal ID (publisher-id): PNAS

Title: Proceedings of the National Academy of Sciences of the United States of America

Publisher: National Academy of Sciences

ISSN (Print): 0027-8424

ISSN (Electronic): 1091-6490

Publication date (Electronic): 9 November 2021

Publication date (Print): 16 November 2021

Publication date PMC-release: 9 November 2021

Volume: 118

Issue: 46

Electronic Location Identifier: e2109481118

Affiliations

[1] ^aDivision of Geological and Planetary Sciences, California Institute of Technology , Pasadena, CA 91125;

[2] ^bJet Propulsion Laboratory, California Institute of Technology , Pasadena, CA 91109;

[3] ^cDivision of Engineering and Applied Science, California Institute of Technology , Pasadena, CA 91125;

[4] ^dDepartment of Chemical and Environmental Engineering, University of California , Riverside, CA 92521;

[5] ^eCenter for Environmental Research and Technology , Riverside, CA 92507;

[6] ^fGoddard Earth Sciences Technology and Research, Universities Space Research Association , Columbia, MD 21046;

[7] ^gGlobal Modeling and Assimilation Office, NASA Goddard Space Flight Center , Greenbelt, MD 20771;

[8] ^hEnergy Research and Development Division, California Energy Commission , Sacramento, CA 95814;

[9] ⁱCooperative Institute for Research in Environmental Sciences, University of Colorado , Boulder, CO 80309;

[10] ^jDepartment of Earth and Planetary Science, University of California , Berkeley, CA 94720;

[11] ^kDepartment of Mechanical Engineering, University of Colorado , Boulder, CO 80309;

[12] ^lDepartment of Climate and Space Sciences and Engineering, University of Michigan , Ann Arbor, MI 48109;

[13] ^mDepartment of Earth System Science, Tsinghua University , Beijing 100084, China;

[14] ⁿDepartment of Atmospheric Sciences, University of Washington , Seattle, WA 98195;

[15] ^oMilken Institute School of Public Health, George Washington University , Washington, DC 20052;

[16] ^pModeling and Meteorology Branch, California Air Resources Board , Sacramento, CA 95814;

[17] ^qDepartment of Chemistry, University of Colorado , Boulder, CO 80309;

[18] ^rCanadian Centre for Climate Modelling and Analysis, Environment and Climate Change Canada , Victoria, BC, V8W 2Y2 Canada;

[19] ^sSchool of Informatics, Computing, and Cyber Systems, Northern Arizona University , Flagstaff, AZ 86011;

[20] ^tScience and Technology Advancement Division, South Coast Air Quality Management District , Diamond Bar, CA, 91765;

[21] ^uDepartment of Environmental Sciences, University of California , Riverside, CA 92521;

[22] ^vDepartment of Physics, University of Toronto , Toronto, ON, M5S 1A1 Canada;

[23] ^wDepartment of Atmospheric and Oceanic Sciences, University of Colorado , Boulder, CO 80309;

[24] ^xInstitute of Arctic and Alpine Research, University of Colorado , Boulder, CO 80309;

[25] ^yMcKelvey School of Engineering, Washington University in St. Louis , St. Louis, MO 63130;

[26] ^zDepartment of Earth and Environmental Sciences, Lamont Doherty Earth Observatory, Columbia University , Palisades, NY 10964;

[27] ^aaBiospheric Sciences Laboratory, NASA Goddard Space Flight Center , Greenbelt, MD 20771;

[28] ^bbThe Earth Institute, Columbia University , New York, NY 10025;

[29] ^ccNicholas School of the Environment, Duke University , Durham, NC 27707;

[30] ^ddJoint Institute for Regional Earth System Science and Engineering, University of California , Los Angeles, CA 90095

Author notes

¹To whom correspondence may be addressed. Email: jlaugh@ 123456caltech.edu , jessica.l.neu@ 123456jpl.nasa.gov , david.schimel@ 123456jpl.nasa.gov , or wennberg@ 123456gps.caltech.edu .

Edited by Akkihebbal R. Ravishankara, Colorado State University, Fort Collins, CO, and approved September 29, 2021 (received for review June 10, 2021)

Author contributions: J.L.L., K.B., K.W.B., A.C., B.E.C., H.L.F., D.K.H., J.K., E.A.K., Z.L., K.M., A.J.T., S.A., J.A., H.C., D.C., J.d.G., A.E., J.C.F., D.L.G., K.R.G., S.H., F.H., C.E.I., D.B.A.J., J.L., N.S.L., R.V.M., G.A.M., L.O., B.P., M.R., S.P.S., N.S., Y.L.Y., and Z.-C.Z. performed research; J.L.N., D.S., and P.O.W. designed research; J.L.L., J.L.N., D.S., P.O.W., K.B., K.W.B., A.C., B.E.C., H.L.F., D.K.H., J.K., E.A.K., Z.L., K.M., A.J.T., S.A., J.A., H.C., D.C., J.d.G., A.E., J.C.F., D.L.G., K.R.G., S.H., F.H., C.E.I., D.B.A.J., J.L., N.S.L., R.V.M., G.A.M., L.O., B.P., M.R., S.P.S., N.S., Y.L.Y., and Z.-C.Z. analyzed data; J.L.L., J.L.N., D.S., and P.O.W. wrote the paper; and K.B., K.W.B., A.C., B.E.C., H.L.F., D.K.H., J.K., E.A.K., Z.L., K.M., A.J.T., S.A., J.A., H.C., D.C., J.d.G., A.E., J.C.F., D.L.G., K.R.G., S.H., F.H., C.E.I., D.B.A.J., J.L., N.S.L., R.V.M., G.A.M., L.O., B.P., M.R., S.P.S., N.S., Y.L.Y., and Z.-C.Z. edited and approved the manuscript draft.

²Present address: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109.

³Present address: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720.

Author information

Joshua L. Laughner https://orcid.org/0000-0002-8599-4555

Kelley Barsanti https://orcid.org/0000-0002-6065-8643

Kevin W. Bowman https://orcid.org/0000-0002-8659-1117

Abhishek Chatterjee https://orcid.org/0000-0002-3680-0160

Bart E. Croes https://orcid.org/0000-0002-9351-0434

Daven K. Henze https://orcid.org/0000-0001-6431-4963

Eric A. Kort https://orcid.org/0000-0003-4940-7541

Alexander J. Turner https://orcid.org/0000-0003-1406-7372

Susan Anenberg https://orcid.org/0000-0002-9668-603X

Hansen Cao https://orcid.org/0000-0003-2713-0430

David Crisp https://orcid.org/0000-0002-4573-9998

Joost de Gouw https://orcid.org/0000-0002-0385-1826

Annmarie Eldering https://orcid.org/0000-0003-1080-9922

Daniel L. Goldberg https://orcid.org/0000-0003-0784-3986

Kevin R. Gurney https://orcid.org/0000-0001-9218-7164

Junjie Liu https://orcid.org/0000-0002-7184-6594

Nicole S. Lovenduski https://orcid.org/0000-0001-5893-1009

Randall V. Martin https://orcid.org/0000-0003-2632-8402

Galen A. McKinley https://orcid.org/0000-0002-4072-9221

Muye Ru https://orcid.org/0000-0003-3252-1030

Stanley P. Sander https://orcid.org/0000-0003-1424-3620

Neil Swart https://orcid.org/0000-0002-8200-6187

Yuk L. Yung https://orcid.org/0000-0002-4263-2562

Zhao-Cheng Zeng https://orcid.org/0000-0002-0008-6508

Article

Publisher ID: 202109481

DOI: 10.1073/pnas.2109481118

PMC ID: 8609622

PubMed ID: 34753820

SO-VID: 98ebb42d-e6dc-4e72-bd19-c4685ad72907

License:

This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).

History

Date accepted : 18 September 2021

Page count

Pages: 12

Funding

Funded by: National Aeronautics and Space Administration (NASA) 100000104

Award ID: NNX17AE15G

Award Recipient : Joshua L Laughner Award Recipient : Paul O. Wennberg Award Recipient : Kevin W. Bowman Award Recipient : Abhishek Chatterjee Award Recipient : Daven K. Henze Award Recipient : Kazuyuki Miyazaki Award Recipient : Susan Anenberg Award Recipient : Hansen Cao Award Recipient : Daniel L Goldberg Award Recipient : Randall V Martin

Funded by: National Aeronautics and Space Administration (NASA) 100000104

Award ID: 80NSSC20K0006

Funded by: National Aeronautics and Space Administration (NASA) 100000104

Award ID: 80NSSC18K0689

Funded by: National Aeronautics and Space Administration (NASA) 100000104

Award ID: 19-AURAST19-0044

Funded by: National Aeronautics and Space Administration (NASA) 100000104

Award ID: 80NSSC20K1122

Funded by: National Science Foundation (NSF) 100000001

Award ID: 2030049

Award Recipient : Kelley Barsanti Award Recipient : Nicole S Lovenduski Award Recipient : Galen A McKinley

Funded by: National Science Foundation (NSF) 100000001

Award ID: OCE-1752724

Award Recipient : Kelley Barsanti Award Recipient : Nicole S Lovenduski Award Recipient : Galen A McKinley

Funded by: National Science Foundation (NSF) 100000001

Award ID: OCE-1948664

Award Recipient : Kelley Barsanti Award Recipient : Nicole S Lovenduski Award Recipient : Galen A McKinley

Funded by: National Science Foundation (NSF) 100000001

Award ID: OCE-1948624

Award Recipient : Kelley Barsanti Award Recipient : Nicole S Lovenduski Award Recipient : Galen A McKinley

Funded by: NASA | Jet Propulsion Laboratory (JPL) 100006196

Award ID: JPL.1613918

Award Recipient : Yuk L. Yung

Funded by: National Aeronautics and Space Administration (NASA) 100000104

Award ID: 80NSSC21K0508

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Societal shifts due to COVID-19 reveal large-scale complexities and feedbacks between atmospheric chemistry and climate change

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Novel Coronavirus Disease COVID-19

Most cited references 70

Temporary reduction in daily global CO2 emissions during the COVID-19 forced confinement

Evolution of organic aerosols in the atmosphere.

The Global Methane Budget 2000–2017

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Cited by 17

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