Global methane emission estimates for 2000–2012 from CarbonTracker Europe-CH<sub>4</sub> v1.0
We present a global distribution of surface methane (CH<sub>4</sub>) emission estimates for 2000–2012 derived using the CarbonTracker Europe-CH<sub>4</sub> (CTE-CH<sub>4</sub>) data assimilation system. In CTE-CH<sub>4</sub>, anthropogenic and biospher...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-03-01
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| Series: | Geoscientific Model Development |
| Online Access: | http://www.geosci-model-dev.net/10/1261/2017/gmd-10-1261-2017.pdf |
| Summary: | We present a global distribution of surface methane
(CH<sub>4</sub>) emission estimates for 2000–2012 derived using the CarbonTracker
Europe-CH<sub>4</sub> (CTE-CH<sub>4</sub>) data assimilation system. In CTE-CH<sub>4</sub>,
anthropogenic and biospheric CH<sub>4</sub> emissions are simultaneously estimated
based on constraints of global atmospheric in situ CH<sub>4</sub> observations.
The system was configured to either estimate only anthropogenic or
biospheric sources per region, or to estimate both categories
simultaneously. The latter increased the number of optimizable parameters
from 62 to 78. In addition, the differences between two numerical schemes
available to perform turbulent vertical mixing in the atmospheric transport
model TM5 were examined. Together, the system configurations encompass
important axes of uncertainty in inversions and allow us to examine the
robustness of the flux estimates. The posterior emission estimates are
further evaluated by comparing simulated atmospheric CH<sub>4</sub> to surface in
situ observations, vertical profiles of CH<sub>4</sub> made by aircraft,
remotely sensed dry-air total column-averaged mole fraction (XCH<sub>4</sub>)
from the Total Carbon Column Observing Network (TCCON), and XCH<sub>4</sub> from
the Greenhouse gases Observing Satellite (GOSAT). The evaluation with
non-assimilated observations shows that posterior XCH<sub>4</sub> is better
matched with the retrievals when the vertical mixing scheme with faster
interhemispheric exchange is used. Estimated posterior mean total global
emissions during 2000–2012 are 516 ± 51 Tg CH<sub>4</sub> yr<sup>−1</sup>, with an
increase of 18 Tg CH<sub>4</sub> yr<sup>−1</sup> from 2000–2006 to 2007–2012. The
increase is mainly driven by an increase in emissions from South American
temperate, Asian temperate and Asian tropical TransCom regions. In addition,
the increase is hardly sensitive to different model configurations
( < 2 Tg CH<sub>4</sub> yr<sup>−1</sup> difference), and much smaller than
suggested by EDGAR v4.2 FT2010 inventory (33 Tg CH<sub>4</sub> yr<sup>−1</sup>), which
was used for prior anthropogenic emission estimates. The result is in good
agreement with other published estimates from inverse modelling studies
(16–20 Tg CH<sub>4</sub> yr<sup>−1</sup>). However, this study could not conclusively
separate a small trend in biospheric emissions (−5 to +6.9 Tg CH<sub>4</sub> yr<sup>−1</sup>)
from the much larger trend in anthropogenic emissions (15–27 Tg CH<sub>4</sub> yr<sup>−1</sup>).
Finally, we find that the global and North American CH<sub>4</sub>
balance could be closed over this time period without the previously
suggested need to strongly increase anthropogenic CH<sub>4</sub> emissions in the
United States. With further developments, especially on the treatment of the
atmospheric CH<sub>4</sub> sink, we expect the data assimilation system presented here
will be able to contribute to the ongoing interpretation of changes in this
important greenhouse gas budget. |
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| ISSN: | 1991-959X 1991-9603 |