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Atmospheric methane in the first decade of the 21st century


IES scientist P. Bergamaschi was the lead author on an article published in the Journal of Geophysical Research, entitled “Atmospheric CH4 in the first decade of the 21st century - Inverse modelling analysis using SCIAMACHY satellite retrievals and NOAA surface measurements”. Other authors included contributors from European and American research institutes and universities, including the Max Planck Institute, NOAA and Harvard University.

Atmospheric methane (CH4), the most important anthropogenic greenhouse gas after carbon dioxide (CO2), has increased significantly since 2007. The causes of this renewed growth are poorly understood and are the subject of intense scientific discussion. This paper analyses global CH4 emissions from 2000-2010 based on inverse modelling using surface observations and satellite measurements. The study finds that global CH4 emissions have increased significantly since 2006 (by 16-20 Tg CH4/yr, equivalent to 3-4% of total emissions), and attributes most of this increase to emissions in the tropics and mid-latitudes of the northern hemisphere, while no significant trend was derived for Arctic latitudes. The increase is mainly attributed to anthropogenic sources, superimposed with significant inter-annual variations (IAV) of CH4 emissions from wetlands and biomass burning.

Various sensitivity experiments showed differences in the detailed latitudinal attribution of derived CH4 emissions, but the IAV and trends averaged over larger latitude bands were reasonably robust.

All sensitivity experiments performed showed in general similar performance compared to a comprehensive dataset of shipboard and airborne observations used for validation, except over Amazonia where satellite retrievals improved agreement with observations in the free troposphere. 

Inter-annual variation of total CH4 emissions derived from the different inversions. The variations are shown relative to the average emissions during the reference period 2003-2005 (12-month running mean values)


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