Methane atmosphere

Elliot, W. P. (1995). On Detecting Long-Term Changes in Atmospheric Moisture. Climadc C/iangc 31 349—367. Etheridge, D. M., et ah (1998). Atmospheric Methane between 1000 A.n. and Present Evidence of... 

Figure 1. Atmospheric methane increases over the last 300 years. Points are annual averages the concentrations before 1960 are from ice core analyses more recent data from atmospheric measurements. From Khalil and Rasmussen (40).

An estimate of the annual methane flux into the atmosphere can be calculated by adding the sinks and the annual increase. These data (Table II) indicate that a flux of 375-475 trillion tons(Tg) per year would be required to account for an annual increase of50-60 trillion tons (7). Estimates of sources of atmospheric methane indicate that up to 83% is biogenic in origin (5). The other abiogenic... 

Concerns over atmospheric methane as a greenhouse gas and the large contribution of biomethanogenesis as a source of this gas make it important to determine the relative significance of various components of this activity. A recent paper (8) summarized estimates (28-30) of source fluxes of atmospheric methane based on several carbon isotopic studies and presented new data on natural sources and biomass burning. These data (Table III) show that of a total flux of 594 million tons (Tg) per year, 83% is produced via biomethanogenesis from a combination of natural (42%) and anthropogenic (41%) sources. 

Chappellaz, ]., Barnola, J. M., Raynaud, D., Korotkevich, Y. S., and Lorius, C. (1990). Atmospheric methane record over the last climatic cycle revealed by the Vostok ice core. Nature 345,127-131. 

This means that the observed change in M mainly reflects a change in the source flux Q or the sink function. As an example we may take the methane concentration in the atmosphere, which in recent years has been increasing by about 0.5% per year. The turnover time is estimated to be about 10 years, i.e., much less than Tobs (200 years). Consequently, the observed rate of increase in atmospheric methane is a direct consequence of a similar rate of increase of emissions into the atmosphere. (In fact, this is not quite true. A fraction of the observed increase is probably due to a decrease in sink strength caused by a decrease in the concentration of hydroxyl radicals responsible for the decomposition of methane in the atmosphere.)... 

The role of carbon dioxide in the Earth s radiation budget merits this interest in atmospheric CO2. There are, however, other changes of importance. The atmospheric methane concentration is increasing, probably as a result of increasing cattle populations, rice production, and biomass burning (Crutzen, 1983). Increasing methane concentrations are important because of the role it plays in stratospheric and... 

Koyama, T. (1963). Gaseous metabolism in lake sediments and paddy soils and the production of atmospheric methane and hydrogen, /. Geophys. Res. 68, 3971-3973. 

Blunier, T., Chappellaz, J. A., Schwander, J. et al. (1993). Atmospheric methane record from a Greenland ice core over the last 1000 years. Geophys. Res. Lett. 20,2219-2222. 

Brook, E. J., Sowers. T., and Orchardo, J. (1996). Rapid variations in atmospheric methane concentration during the past 110 000 years. Science 273, 1087-1091. 

Dlugokencky, K., Masarie, A., Lang, P. M., and Tans, P. P. (1998). Continuing decline in the growth rate of the atmospheric methane burden. Nature 393, 447-450. 

Rasmussen, R. A. and Khalil, M. A. K. (1984). Atmospheric methane in recent and ancient atmospheres Concentrations, trends, and interhemispheric gradient. /. Geophys. Res. 89,11599-11604. 

Sass RL, Cicerone RJ. Photosynthate allocations in rice plants food production or atmospheric methane Proc. Natl. Acad. Sci. USA 2002 99 11993-11995. 

Cicerone RJ, Shetter JD. Sources of atmospheric methane Measurements in rice paddies and a discussion. J. Geophys. Res. 1981 86 7203-7209. 

Indexes o and s define the ratio of the carbon isotopes in the sample and in the standard. A lithospheric carbonate material was accepted as standard. The closest to this zero point value belongs to standard sample NBS-19 (1.95%c). There are some other standard samples NBS-22 oil (—29.74%c), NBS-18 calcium carbonate (— 5.01%c). Usually 813C values for plants are in the range ( 15%o) to (— 30%c), and for oil (— 20%c) to ( 36%c). Atmospheric methane has the lowest content of 13C. Its 813C value is approximately —47%o. 

Although atmospheric methane concentrations appear to have stabilized over the past few decades, melting of gas hydrates in permafrost and shallow marine sediments have the potential to rapidly release large quantities of this potent greenhouse gas. As noted in... 

Hein R, Crutzen PJ, Heimann M. 1997. An inverse modeling approach to investigate the global atmospheric methane cycle. Global Bio geochemical Cycles 11 43-76. 

LeUeveld I, Crutzen PI, Dentener FI. 1998. Changing concentration, lifetime and climate forcing of atmospheric methane. Tellus Series B-Chemical and Physical Meteorology 50 128-150. 

Methane is a minor, bnt important, constitnent of onr atmosphere, contribnting abont 1.7 parts per million (ppm). Methane is the second most important greenhonse gas, after carbon dioxide, in onr atmosphere. Atmospheric methane comes mainly from three sonrces ... 

Atmospheric methane has a mean 5 C-value of around —47%c (Stevens 1988). Quay et al. (1999) presented global time series records between 1988 and 1995 on the carbon and hydrogen isotope composition of atmospheric methane. They measured spatial and temporal variation in and D with a slight emichment observed for the southern hemisphere (—47.2%c) relative to the northern hemisphere (—47.4%o). The mean 5D was —86 3%c with a 10%o depletion in the northern relative to the southern hemisphere. 

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