Global posterior estimates using GOSAT and/or surface measurements are between 510–516 Tg yr−1, which is less than, though within the uncertainty of, the prior global flux of 529 ± 25 Tg yr−1. To test if karst is systematically acting as a global CH4 sink, we measured the CH4 concentrations, δ13CCH4, and δ2HCH4 values of cave air from 33 caves in the USA and three caves in New Zealand. This limitation severely restricts our ability to model global wetland CH4 emissions with confidence. Agreement between the models improves for zonally summed CH4 emissions, but large variation between the models remains. Changes in OH radicals during 2006–2008 are found to be less than 1% in inversions, with only a small impact on the inferred methane emissions. Anthropogenic methane production, however, can cause methane concentrations to increase more quickly than they are offset by sinks. We find that a collocation window of ±750 km and ±24 h does not introduce significant error in comparing TES and aircraft profiles. First, the suite of models demonstrate extensive disagreement in their simulations of wetland areal extent and CH4 emissions, in both space and time. For annual global CH4 emissions, the models vary by ±40% of the all-model mean (190 Tg CH4 yr−1). The source anomaly in 2008 is found to be much larger in the wetland ecosystem model than in the inversions, suggesting a too strong sensitivity of bottom-up modeled emissions to precipitation. The primary natural sink for methane is the atmosphere itself; another natural sink is soil, where methane is oxidized by bacteria. This result is consistent with some bottom-up emissions inventories but not with recent estimates based on atmospheric ethane. The DE08 record shows that methane growth rates have generally increased since the onset of the industrial revolution to a level of 14 ppbv year -1 (about 1% per year) by the 1970s. �����[���ܬ���Q�##&�� G���t՝����?gvv�t��u�?��� �F�S���Z�/����O��p��? by the B-U approach is considered more likely because it is a robust feature satellite-derived extent of inundated areas. CH4 concentrations and δ13CCH4 and δ2HCH4 values suggest that microbial methanotrophy within caves is the primary CH4 consumption mechanism as the atmosphere exchanges with subsurface air. As with CO 2, human activity is increasing the CH 4 concentration faster than it can be offset by natural sinks. Global emissions derived from inversions are found to have increased by 19 Tg on average in 2007 (16 to 21 Tg) and by 13 Tg in 2008 (6 to 20 Tg), as compared to the 1999–2006 period. Although processed-based models have their own Over the whole period we infer an increase of global ecosystem CH4 emissions of +1.11 Tg CH4 yr−1, not considering potential additional changes in wetland extent. %���� minima between −41 and −19 Tg yr−1 in 1992) and during the alternate 1997–1998 Our successful validation of V005 encourages its production as a standard retrieval to replace V004. Further, the inversion estimates a decrease in biomass-burning emissions that could explain falling ethane abundance. Only 5 locations from 3 caves showed elevated CH4 concentrations compared to the atmospheric background and could be ascribed to local CH4 sources from sewage and outgassing swamp water. atmosphere, the top-down and bottom-up approaches agree on the fact that IPCC Expert Meeting /... Atmospheric methane isotopic record favors fossil sources flat in 1980s and 1990s with recent increa... Atmospheric methane evolution the last 40 years, Increasing boreal wetland emissions inferred from reductions in atmospheric CH4 seasonal cycle, Stable atmospheric methane in the 2000s: key-role of emissions from natural wetlands. As with most global models, CLM4 lacks important features for predicting current and future CH4 fluxes, including: vertical representation of soil organic matter, accurate subgrid scale hydrology, realistic representation of inundated system vegetation, anaerobic decomposition, thermokarst dynamics, and aqueous chemistry. We compared the seasonality and magnitude of predicted CH4 emissions to observations from 18 sites and three global atmospheric inversions. The ice chronology was determined from the observed chemical and isotopic seasonal variations, verified against a volcanic horizon. We find using a series of numerical experiments using the TM5 atmospheric chemistry transport model that increasing wetland emissions and/or decreasing fossil fuel emissions can explain these observed changes, but no significant role for trends in meteorology and tropical wetlands. Even when V005 cannot retrieve two pieces of information it still performs better than V004. Together with more modern records of isotopic atmospheric CH4, we performed a time-dependent retrieval of methane fluxes spanning 25 y (1984-2009) using a 3D chemical transport model. The observed growth after 2006 is overestimated by the model in all regions. process-discriminating inversion whereas a positive trend (+1.3 ± 0.3 Tg yr−1) In our simulations, the CH4 lifetime decreases by more than 8 % from 1970 to 2012, a significant shortening of the residence time of this important greenhouse gas. The atmospheric inversions are constrained by the atmospheric CH4 observations of the SCIAMACHY satellite instrument and global surface networks. Among these caves, 35 exhibited subatmospheric CH4 concentrations in at least one location compared to their local atmospheric backgrounds. The extracted ice-core air was analysed for methane using gas chromatography with flame-ionisation detection.
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