Abstract
AbstractWe present an assessment of methane (CH4) atmospheric concentrations over the Amazon Basin for 2010 and 2011 using a 3‐D atmospheric chemical transport model, two wetland emission models, and new observations made during biweekly flights made over four locations within the basin. We attempt to constrain basin‐wide CH4 emissions using the observations, and since 2010 was an unusually dry year, we assess the effect of this drought on Amazonian methane emissions. We find that South American emissions contribute up to 150 ppb to concentrations at the sites, mainly originating from within the basin. Our atmospheric model simulations agree reasonably well with measurements at three of the locations (0.28 ≤ r2 ≤ 0.63, mean bias ≤ 9.5 ppb). Attempts to improve the simulated background CH4 concentration through analysis of simulated and observed sulphur hexafluoride concentrations do not improve the model performance, however. Through minimisation of seasonal biases between the simulated and observed atmospheric concentrations, we scale our prior emission inventories to derive total basin‐wide methane emissions of 36.5–41.1 Tg(CH4)/yr in 2010 and 31.6–38.8 Tg(CH4)/yr in 2011. These totals suggest that the Amazon contributes significantly (up to 7%) to global CH4 emissions. Our analysis indicates that factors other than precipitation, such as temperature variations or tree mortality, may have affected microbial emission rates. However, given the uncertainty of our emission estimates, we cannot say definitively whether the noncombustion emissions from the region were different in 2010 and 2011, despite contrasting meteorological conditions between the two years.
Highlights
Methane (CH4) is a powerful greenhouse gas that is emitted into the atmosphere from a variety of anthropogenic and natural sources
We present an assessment of methane (CH4) atmospheric concentrations over the Amazon
Each site displays a distinct pattern of temporal variation and no site displays an obvious seasonal cycle, the majority of the enhancements to CH4 concentration generally occur between March and October
Summary
Methane (CH4) is a powerful greenhouse gas that is emitted into the atmosphere from a variety of anthropogenic and natural sources. Due to the sensitivity of wetland emissions to climate factors such as temperature and precipitation, these emissions may significantly affect the interannual variation of atmospheric CH4 [Fung et al, 1991; Bousquet et al, 2006; Kirschke et al, 2013; Pison et al, 2013]. Due partly to the variable contribution of these natural sources, along with variations in climate [Rigby et al, 2008] and the relatively short lifetime of CH4 (9–11 years) [Prinn et al, 2005; Fiore et al, 2008; Prather et al, 2012], the annual growth rate of atmospheric methane varies significantly over short time scales (e.g., a few years). As well as the partitioning of emissions between different source types, are not well constrained, and several hypotheses have been proposed to explain the recent
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