Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions
<p>We use the GEOS-Chem global 3-D model and two inverse methods (the maximum a posteriori and ensemble Kalman filter) to infer regional methane (CH<span class="inline-formula"><sub>4</sub></span>) emissions and the corresponding stable-carbon-isotope source s...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2023-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/8429/2023/acp-23-8429-2023.pdf |
| _version_ | 1797770713427345408 |
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| author | A. Drinkwater A. Drinkwater P. I. Palmer P. I. Palmer L. Feng L. Feng T. Arnold T. Arnold X. Lan X. Lan S. E. Michel R. Parker R. Parker H. Boesch H. Boesch |
| author_facet | A. Drinkwater A. Drinkwater P. I. Palmer P. I. Palmer L. Feng L. Feng T. Arnold T. Arnold X. Lan X. Lan S. E. Michel R. Parker R. Parker H. Boesch H. Boesch |
| author_sort | A. Drinkwater |
| collection | DOAJ |
| description | <p>We use the GEOS-Chem global 3-D model and two inverse methods (the
maximum a posteriori and ensemble Kalman filter) to infer
regional methane (CH<span class="inline-formula"><sub>4</sub></span>) emissions and the corresponding stable-carbon-isotope source signatures from 2004–2020 across the globe using
in situ and satellite remote sensing data.
We use the Siegel estimator to determine linear trends from the in situ data. Over our 17-year study period, we estimate a linear
increase of 3.6 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> in CH<span class="inline-formula"><sub>4</sub></span> emissions from tropical continental
regions, including North Africa, southern Africa, tropical South America, and tropical
Asia. The second-largest increase in CH<span class="inline-formula"><sub>4</sub></span> emissions over this period (1.6 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>) is from China. For boreal regions we estimate a
negative emissions trend of <span class="inline-formula">−</span>0.2 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>, and for northern and southern
temperate regions we estimate trends of 0.03 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> and
0.2 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>, respectively.
These increases in CH<span class="inline-formula"><sub>4</sub></span> emissions are accompanied by a progressively
isotopically lighter atmospheric <span class="inline-formula"><i>δ</i><sup>13</sup></span>C signature over the
tropics, particularly since 2012, which is consistent with an
increased biogenic emissions source and/or a decrease in a
thermogenic/pyrogenic emissions source with a heavier isotopic signature.
Previous studies have linked increased tropical biogenic emissions to
increased rainfall. Over China, we find a weaker trend towards isotopically lighter
<span class="inline-formula"><i>δ</i><sup>13</sup></span>C sources, suggesting that heavier isotopic source
signatures make a larger contribution to this region.
Satellite remote sensing data provide additional evidence of emissions
hotspots of CH<span class="inline-formula"><sub>4</sub></span> that are consistent with the location and seasonal
timing of wetland emissions.
The collective evidence suggests that increases in tropical CH<span class="inline-formula"><sub>4</sub></span>
emissions are from biogenic sources, with a significant fraction from
wetlands.
To understand the influence of our results on changes in the hydroxyl
radical (OH), we also report regional CH<span class="inline-formula"><sub>4</sub></span> emissions estimates using
an alternative scenario of a 0.5 % yr<span class="inline-formula"><sup>−1</sup></span> decrease in OH since 2004,
followed by a larger 1.5 % drop in 2020 during the first COVID-19
lockdown.
We find that our main findings are broadly insensitive to those
idealised year-to-year changes in OH, although the corresponding
change in atmospheric CH<span class="inline-formula"><sub>4</sub></span> in 2020 is inconsistent with independent
global-scale constraints for the estimated annual-mean atmospheric
growth rate.</p> |
| first_indexed | 2024-03-12T21:26:12Z |
| format | Article |
| id | doaj.art-f533d6bea0d349deb4c76aa7fcb97ff7 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-03-12T21:26:12Z |
| publishDate | 2023-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-f533d6bea0d349deb4c76aa7fcb97ff72023-07-28T08:44:12ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242023-07-01238429845210.5194/acp-23-8429-2023Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissionsA. Drinkwater0A. Drinkwater1P. I. Palmer2P. I. Palmer3L. Feng4L. Feng5T. Arnold6T. Arnold7X. Lan8X. Lan9S. E. Michel10R. Parker11R. Parker12H. Boesch13H. Boesch14School of GeoSciences, University of Edinburgh, Edinburgh, UKNational Physical Laboratory, Teddington, UKSchool of GeoSciences, University of Edinburgh, Edinburgh, UKNational Centre for Earth Observation, University of Edinburgh, Edinburgh, UKSchool of GeoSciences, University of Edinburgh, Edinburgh, UKNational Centre for Earth Observation, University of Edinburgh, Edinburgh, UKSchool of GeoSciences, University of Edinburgh, Edinburgh, UKNational Physical Laboratory, Teddington, UKCooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USAGlobal Monitoring Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USAInstitute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, CO, USANational Centre for Earth Observation, Space Park Leicester, University of Leicester, Leicester, UKEarth Observation Science, School of Physics and Astronomy, University of Leicester, Leicester, UKNational Centre for Earth Observation, Space Park Leicester, University of Leicester, Leicester, UKEarth Observation Science, School of Physics and Astronomy, University of Leicester, Leicester, UK<p>We use the GEOS-Chem global 3-D model and two inverse methods (the maximum a posteriori and ensemble Kalman filter) to infer regional methane (CH<span class="inline-formula"><sub>4</sub></span>) emissions and the corresponding stable-carbon-isotope source signatures from 2004–2020 across the globe using in situ and satellite remote sensing data. We use the Siegel estimator to determine linear trends from the in situ data. Over our 17-year study period, we estimate a linear increase of 3.6 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> in CH<span class="inline-formula"><sub>4</sub></span> emissions from tropical continental regions, including North Africa, southern Africa, tropical South America, and tropical Asia. The second-largest increase in CH<span class="inline-formula"><sub>4</sub></span> emissions over this period (1.6 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>) is from China. For boreal regions we estimate a negative emissions trend of <span class="inline-formula">−</span>0.2 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>, and for northern and southern temperate regions we estimate trends of 0.03 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span> and 0.2 Tg yr<span class="inline-formula"><sup>−1</sup></span> yr<span class="inline-formula"><sup>−1</sup></span>, respectively. These increases in CH<span class="inline-formula"><sub>4</sub></span> emissions are accompanied by a progressively isotopically lighter atmospheric <span class="inline-formula"><i>δ</i><sup>13</sup></span>C signature over the tropics, particularly since 2012, which is consistent with an increased biogenic emissions source and/or a decrease in a thermogenic/pyrogenic emissions source with a heavier isotopic signature. Previous studies have linked increased tropical biogenic emissions to increased rainfall. Over China, we find a weaker trend towards isotopically lighter <span class="inline-formula"><i>δ</i><sup>13</sup></span>C sources, suggesting that heavier isotopic source signatures make a larger contribution to this region. Satellite remote sensing data provide additional evidence of emissions hotspots of CH<span class="inline-formula"><sub>4</sub></span> that are consistent with the location and seasonal timing of wetland emissions. The collective evidence suggests that increases in tropical CH<span class="inline-formula"><sub>4</sub></span> emissions are from biogenic sources, with a significant fraction from wetlands. To understand the influence of our results on changes in the hydroxyl radical (OH), we also report regional CH<span class="inline-formula"><sub>4</sub></span> emissions estimates using an alternative scenario of a 0.5 % yr<span class="inline-formula"><sup>−1</sup></span> decrease in OH since 2004, followed by a larger 1.5 % drop in 2020 during the first COVID-19 lockdown. We find that our main findings are broadly insensitive to those idealised year-to-year changes in OH, although the corresponding change in atmospheric CH<span class="inline-formula"><sub>4</sub></span> in 2020 is inconsistent with independent global-scale constraints for the estimated annual-mean atmospheric growth rate.</p>https://acp.copernicus.org/articles/23/8429/2023/acp-23-8429-2023.pdf |
| spellingShingle | A. Drinkwater A. Drinkwater P. I. Palmer P. I. Palmer L. Feng L. Feng T. Arnold T. Arnold X. Lan X. Lan S. E. Michel R. Parker R. Parker H. Boesch H. Boesch Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions Atmospheric Chemistry and Physics |
| title | Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions |
| title_full | Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions |
| title_fullStr | Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions |
| title_full_unstemmed | Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions |
| title_short | Atmospheric data support a multi-decadal shift in the global methane budget towards natural tropical emissions |
| title_sort | atmospheric data support a multi decadal shift in the global methane budget towards natural tropical emissions |
| url | https://acp.copernicus.org/articles/23/8429/2023/acp-23-8429-2023.pdf |
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