• DOI:10.5194/ACP-19-14721-2019
• Corpus ID: 198448426

An increase in methane emissions from tropical Africa between 2010 and 2016 inferred from satellite data

@article{Lunt2019AnII,
  title={An increase in methane emissions from tropical Africa between 2010 and 2016 inferred from satellite data},
  author={Mark F. Lunt and Paul I. Palmer and Liang Feng and Christopher M. Taylor and Hartmut Boesch and Robert J. Parker},
  journal={Atmospheric Chemistry and Physics},
  year={2019}
}

• M. Lunt, P. Palmer, +3 authors R. Parker
• Published 26 June 2019
• Environmental Science
• Atmospheric Chemistry and Physics

Abstract. Emissions of methane (CH4) from tropical ecosystems, and how they
respond to changes in climate, represent one of the biggest
uncertainties associated with the global CH4 budget. Historically,
this has been due to the dearth of pan-tropical in situ measurements,
which is particularly acute in Africa. By virtue of their superior
spatial coverage, satellite observations of atmospheric CH4
columns can help to narrow down some of the uncertainties in the
tropical CH4 emission budget. We use proxy column retrievals of
atmospheric CH4 (XCH4) from the Japanese Greenhouse gases
Observing Satellite (GOSAT) and the nested version of the GEOS-Chem
atmospheric chemistry and transport model
(0.5∘×0.625∘) to infer emissions from tropical
Africa between 2010 and 2016. Proxy retrievals of XCH4 are less
sensitive to scattering due to clouds and aerosol than full physics retrievals, but the method assumes
that the global distribution of carbon dioxide (CO2) is known. We
explore the sensitivity of inferred a posteriori emissions to
this source of systematic error by using two different XCH4 data
products that are determined using different model CO2 fields. We
infer monthly emissions from GOSAT XCH4 data using a hierarchical
Bayesian framework, allowing us to report seasonal cycles and trends
in annual mean values. We find mean tropical African emissions between 2010 and 2016 range
from 76 (74–78) to 80 (78–82) Tg yr−1,
depending on the proxy XCH4 data used, with larger differences in
Northern Hemisphere Africa than Southern Hemisphere Africa. We find a
robust positive linear trend in tropical African CH4 emissions for our 7-year study period, with values of 1.5 (1.1–1.9) Tg yr−1
or 2.1 (1.7–2.5) Tg yr−1, depending on the CO2 data
product used in the proxy retrieval. This linear emissions trend accounts for around a third of the global emissions growth rate during this period. A substantial portion of this increase is due to a short-term increase in emissions of 3 Tg yr−1 between 2011 and 2015 from the Sudd in South Sudan. Using satellite land surface temperature anomalies and altimetry data, we find this increase in CH4 emissions is consistent with an increase in wetland extent due to increased inflow from the White Nile, although the data indicate that the Sudd was anomalously dry at the start of our inversion period. We find a strong seasonality in emissions across Northern Hemisphere Africa, with the timing of the seasonal emissions peak coincident with the seasonal peak in ground water storage. In contrast, we find that a posteriori CH4 emissions from the wetland area of the Congo Basin are approximately constant throughout the year, consistent with less temporal variability in wetland extent, and significantly smaller than a priori estimates.