Showing papers on "Atmospheric methane published in 1983"

Sources, sinks, and seasonal cycles of atmospheric methane

Abstract: It is shown that a lifetime of approximately 8 years is most consistent with the observed latitudinal variation of atmospheric methane, requiring the current global emissions of methane to be around 550 teragrams per year. The repeating pattern of a rapid rise of CH4 concentrations in the fall in the Northern Hemisphere indicates a large fall source at latitudes above 30 deg N. The remaining observed seasonal variations are seen as consistent with the seasonal cycle of OH, which removes methane from the atmosphere. An extensive set of self-consistent measurements of methane is reported and analyzed, revealing that methane has increased during the past 3-4 years at rates of 1-1.9 percent per year all over the world at sites ranging from inside the Arctic Circle to the South Pole. The observational results are used in estimating the sources, sinks, and seasonal cycles of CH4 and the effects of human activities on its atmospheric abundance.

Seasonal variation of methane flux from a California rice paddy

Abstract: To allow increased understanding of the global budget of atmospheric methane, individual methane sources require investigation. We have measured methane emissions from a California rice paddy during the entire 1982 growing season. A very strong seasonal dependence was observed. Methane emissions were highest in the last 2–3 weeks before harvest; daily emissions reached 5 g CH4/m2. Over the 100-day season, daily emissions averaged about 0.25 g CH4/m2, higher than our previously reported values. Attempts to estimate global rice paddy emissions must recognize the possibility of seasonal variations. Soil temperature at 10-cm depth correlated poorly with our measured fluxes; soil redox potential was a more reliable indicator.

Production of nitrous oxide and consumption of methane by forest soils

Abstract: Soils in an Amazonian rainforest are observed to release N2O at a rate larger than the global mean by about a factor of 20. Emissions from a New England hardwood forest are approximately 30 times smaller then Brazilian values. Atmospheric methane is consumed by soils in both systems. Tropical forests would provide a major source of atmospheric N2O if the Brazilian results are representative.

Global production of methane by termites

Abstract: Widespread destruction of forests and their replacement by grasslands may provide suitable habitats for termites, leading to an increase in their population and thus also in the production of methane1. We have carried out an experiment to verify the role of termites in the global methane cycle and to identify the uncertainties inherent in such global extrapolations of laboratory data. We found that termites are indeed a potentially significant source of atmospheric methane with an estimated global prodution of about 50 × 1012 g yr−1; however, the uncertainties in global estimates are so large (10–100 × 1012 g yr−1) that it cannot yet be proved that termites play an important role in the global methane cycle. Our calculations show that the production of CH4 by termites is probably <15% of the global yearly emissions.

The many origins of natural gas

Abstract: Thermodynamic calculations for the C-O-S-H system indicate that at a fixed oxygen fugacity methane is in a stable phase relative to carbon dioxide at high pressures and low temperatures. At a constant temperature and pressure, methane is favored at low oxygen fugacities. Volcanic gases and near-surface igneous rocks exhibit high values of oxygen fugacity. However, direct measurement of the oxygen fugacity of spinels from peridotites of deep origin indicate that the oxygen fugacity of these rocks is low, corresponding to an iron - wustite buffer. The relative abundance of the carbon isotopes C12 and C13 varies widely in natural gases. Methane formed by bacterial fermentation is highly enriched in the lighter isotope, while methane from deep deposits is much less so as is the methane flowing from hydrothermal vents on the East Pacific Rise. Except In extreme cases, the carbon isotope ratio cannot be used alone to assess whether methane is biogenic or abiogenic. The carbon isotope ratio in coexisting methane and carbon dioxide can be used to estimate the temperature at which the two gases came into isotopic equilibrium. This ratio indicates a high temperature of equilibration for a number of gas deposits. The carbon and helium isotope ratios together with their geologic settings are strongly suggestive that the large quantities of methane in Lake Kivu and the gases venting along the East Pacific Rise are abiogenic. Methane associated with the Red Sea brines and various geothermal areas may also be in part abiogenic. The high abundance of carbon in the Sun, the atmosphere of the outer planets, carbonaceous chondrites and comets, suggests that carbon may be more abundant in the Earth than it is in near-surface igneous rocks. Such a high abundance could lead to a progressive outgassing of methane at depth, which then is oxidized near the surface or in the atmosphere. Methane hydrates are stable at low temperatures and high pressures. Today, methane hydrates are found in areas of permafrost and in ocean sediments. Methane hydrates in ocean sediments were first formed about 20 mya (million years ago) when the Antarctic ice sheet reached sea level. Terrestrial methane hydrates formed more recently during the glaciations beginning 1.6 mya. Methane hydrates and trapped gas are probably abundant under the Antarctic ice sheet. The formation of methane hydrates may be related to the low values of carbon dioxide in the atmosphere some 20,000 years ago.

Impact of a global warming on biospheric sources of methane and its climatic consequences

Abstract: Most of atmospheric methane originates by bacterial processes in anaerobic environments withinthe soil which are found to become more productive with increases in ambient temperature. Awarming of climate, due to increasing levels of industrial gases resulting from fossil fuel burning,is thus likely to increase methane abundance within the atmosphere. This may lead to furtherheating of the atmosphere, since both methane and ozone (which is generated in the tropospherefrom reactions of methane) have greenhouse effects. We have explored this feedback mechanismusing a coupled climate-chemical model of the troposphere, by calculating the impact of thepredicted global warming due to iricreased emissions of carbon dioxide and other industrial gaseson the biospheric sources of methane. Although we find this climate feedback to be, by itself,relatively minor, it can produce measurable increases in atmospheric CH 4 , concentration, aquantity which should additionally increase as a consequence of increasing anthropogenicemissions of CO and CH 4 , itself. It would thus seem useful to carefully monitor futureatmospheric CH 4 , concentrations. DOI: 10.1111/j.1600-0889.1983.tb00001.x

Increasing atmospheric methane

Abstract: Variations des concentrations du methane dans l'atmosphere a court terme et comparees aux analyses du methane piege dans les glaces polaires