Atmospheric methane

About: Atmospheric methane is a research topic. Over the lifetime, 2034 publications have been published within this topic receiving 119616 citations.

Methane flux dynamics in an Irish lowland blanket bog

Abstract: Pristine peatlands are a significant source of atmospheric methane (CH4) Large spatio–temporal variation has been observed in flux rates within and between peatlands Variation is commonly associated with water level, vegetation structure, soil chemistry and climatic variability We measured spatial and temporal variation in CH4 fluxes in a blanket bog during the period 2003–2005 The surface of the bog was composed of different vegetation communities (hummocks, lawns and hollows) along a water level gradient CH4 fluxes were measured in each community using a chamber method Regression modelling was used to relate the fluxes with environmental variables and to integrate fluxes over the study period Water level was the strongest controller of spatial variation; the average flux rate was lowest in hummocks and highest in hollows, ranging from 3 to 53 mg CH4 m−2 day−1 In vegetation communities with a permanently high water level, the amount and species composition of vegetation was also a good indicator of flux rate We observed a clear seasonal variation in flux that was chiefly controlled by temperature The annual average flux (62 g CH4 m−2 year−1) was similar to previous estimates from blanket bogs and continental raised bogs No interannual variation was observed

Stratospheric ozone depletion at northern mid latitudes in the 21st century: The importance of future concentrations of greenhouse gases nitrous oxide and methane

Abstract: [1] There is evidence that the halogen loading of the atmosphere has peaked and stratospheric ozone levels are expected to recover to pre-1980 levels this century. However, N2O concentrations in the atmosphere are increasing, resulting in increasing levels of NOx in the stratosphere. In addition, the growth rate in the atmospheric methane burden has declined in recent years, leading to the suggestion that methane emissions have stabilized. A 2-D chemical transport model is used to calculate stratospheric ozone from 2000 to 2100 for a range of IPCC scenarios. The model predicts that mid-latitude stratospheric ozone will recover only partially towards pre-1980 levels over the next 50 years, but will then decline, largely due to increases in stratospheric NOx. If greenhouse gas mitigation strategies result in lower future methane levels, mid-latitude stratospheric ozone levels in 2100 are predicted to be lower than current values, particularly in late summer and autumn.

Attention turns to naturally occurring methane seepage

Abstract: Methane is the most abundant organic compound in the Earth's atmosphere. As a powerful greenhouse gas, it has implications for global climate change. Sources of methane to the atmosphere are varied. Depending on the source, methane can contain either modern or ancient carbon. Methane exiting from swamps and wetlands contains modern carbon, whereas methane leaking from petroleum reservoirs contains ancient carbon. The total annual source of methane to the atmosphere has been constrained to about 540 teragrams (Tg) per year “Cicerone and Oremland, 1988”. Notably absent from any identified sources is the contribution of geologically sourced methane from naturally occurring seepage.

Methane flux and stable hydrogen and carbon isotope composition of sedimentary methane from the Florida Everglades

Abstract: Methane flux and the stable isotopic composition of sedimentary methane were measured at four locations in the Florida Everglades system. Individual estimates of methane flux ranged over more than 3 orders of magnitude, from about 0.001 to 2.6 g CH4 m−2 d−1. Significant interstation differences in total methane flux were also observed and are judged most likely attributable to differences in the size and spacing of emergent aquatic vegetation, and possibly differences in the type (i.e., vascular plant versus algal) of organic matter incorporated into the sediments. On the basis of measurements presented here and by other investigators, the Everglades system appears to be a relatively weak source of atmospheric methane, probably contributing less than 0.5 Tg CH4 yr−1. Emergent aquatic plants appear to be capable of indirectly affecting the stable isotopic composition of sedimentary methane by stimulating methane oxidation via root aeration. A significant positive correlation between δD-CH4 and δ13C-CH4 was observed for samples collected from sediments covered by tall, dense stands of emergent plants. In contrast, a significant negative correlation between the δD and δ13C of sedimentary methane was observed for samples collected at an open water site where ebullition dominated methane transfer to the atmosphere. The mean δ13C of sedimentary methane samples measured in the Everglades system (mean δ13C =−61.7‰, s.d. = 3.6‰, n = 51) is not significantly different from the estimated average δ13C of all natural sources (−58.3‰). The mean δD of Everglades sedimentary methane (mean δ D = −293‰, s.d. = 14‰, n = 50) appears to be slightly less D-depleted than the estimated average methane (δD =−360 ± 30‰) from all sources.

Four-dimensional variational data assimilation for inverse modeling of atmospheric methane emissions: Analysis of SCIAMACHY observations

Abstract: Recent observations from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) instrument aboard ENVISAT have brought new insights in the global distribution of atmospheric methane. In particular, the observations showed higher methane concentrations in the tropics than previously assumed. Here, we analyze the SCIAMACHY observations and their implications for emission estimates in detail using a four-dimensional variational (4D-Var) data assimilation system. We focus on the period September to November 2003 and on the South American continent, for which the satellite observations showed the largest deviations from model simulations. In this set-up the advantages of the 4D-Var approach and the zooming capability of the underlying TM5 atmospheric transport model are fully exploited. After application of a latitude-dependent bias correction to the SCIAMACHY observations, the assimilation system is able to accurately fit those observations, while retaining consistency with a network of surface methane measurements. The main emission increments resulting from the inversion are an increase in the tropics, a decrease in South Asia, and a decrease at northern hemispheric high latitudes. The SCIAMACHY observations yield considerable additional emission uncertainty reduction, particularly in the (sub-)tropical regions, which are poorly constrained by the surface network. For tropical South America, the inversion suggests more than a doubling of emissions compared to the a priori during the 3 months considered. Extensive sensitivity experiments, in which key assumptions of the inversion set-up are varied, show that this finding is robust. Independent airborne observations in the Amazon basin support the presence of considerable local methane sources. However, these observations also indicate that emissions from eastern South America may be smaller than estimated from SCIAMACHY observations. In this respect it must be realized that the bias correction applied to the satellite observations does not take into account potential regional systematic errors, which - if identified in the future - will lead to shifts in the overall distribution of emission estimates.