Showing papers on "Atmospheric methane published in 1989"
TL;DR: Model calculations of source partitioning based on the carbon-14 data, CH4 concentrations, and δ13C in CH4 indicate that 21 � 3% of atmospheric CH4 was derived from fossil carbon at the end of 1987, and data indicate that pressurized water reactors are an increasingly important source of 14CH4.
Abstract: Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric (14)GH(4) seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 +/- 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 +/- 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH(4) concentrations, and delta(13)C in CH(4) indicate that 21 +/- 3% of atmospheric CH(4) was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of (14)CH(4).
235 citations
TL;DR: In this paper, it is shown from modeling of mesospheric ice-particle formation that noctilucent cloud brightness should be a sensitive indicator of the water content at the high-latitude summertime mesopause.
Abstract: The possiblity is investigated that a substantial change has occurred in middle-atmospheric water vapor as a result of the increase in atmospheric methane over the past century and a half. It is shown from modeling of mesospheric ice-particle formation that noctilucent cloud brightness should be a sensitive indicator of the water content at the high-latitude summertime mesopause. From an examination of the historical record of noctilucent cloud occurrence, it is found that such clouds are absent from the record before 1885, a finding which is consistent with the hypothesis proposed in this paper.
220 citations
106 citations
TL;DR: In this article, the authors examined the energy balance in the atmosphere and concluded that the temperature near 1 μbar is ∼100K rather than the surface temperature; consequently, the mean molecular weight of the atmosphere is close to 25a.m.u.
Abstract: THE recent occultation of a 12th magnitude star by Pluto provided a unique opportunity for studying its atmosphere. Analyses of measurements made at the Hobart observatory in Australia and the Kuiper Airborne Observatory (KAO) have been published1,2. It is generally agreed that Pluto possesses a substantial atmosphere, with a surface pressure of ∼l0µbar. Both occultation measurements are sensitive primarily to the atmospheric conditions at the 1-μbar level. Analysis of the Hobart data reveals an atmospheric scale height of 46–57 km at a radial distance of 1,240–1,290 km, whereas the scale height derived from the KAO data is 59.7 ± 1.5 km at 1,214 ± 20 km. The existence of an optically thick dust layer along the line of sight at the limb has been inferred from the KAO measurements, raising doubts about the true surface radius of Pluto2. The measured scale heights are consistent with a purely methane atmosphere at a temperature of 50–61 K for the Hobart data1 and 67±6K for the KAO data2. These values are close to the surface temperature3. Here we examine the energy balance in the atmosphere and conclude that the temperature near 1 μ bar is ∼100K rather than the surface temperature; consequently, the mean molecular weight of the atmosphere is close to 25a.m.u., and a molecule heavier than (and in addition to) methane must be present in the atmosphere.
85 citations
TL;DR: In this article, it was shown that the response of wetlands and permafrost may add as much or more methane and nitrous oxide to the atmosphere as expected from the increasing anthropogenic sources.
Abstract: Recent experiments have shown that the concentrations of methane dipped to between 300 and 350 ppbv during the ice ages some 20,000 and 150,000 years ago. Our data, spanning more recent times, show a proportionate decrease of methane (38 ± 19 ppbv) and also a decrease of nitrous oxide (about 6 ± 4 ppbv) during the little ice age between 1450 and 1750 AD. We believe that these decreases are a measure of the response of emissions from the earth's soils, oceans, and wetlands to global climatic change. In the future, as the earth warms from increasing levels of carbon dioxide, methane, nitrous oxide, and other trace gases, these feedbacks may produce more and more methane and nitrous oxide. Melting of the upper layers of permafrost in the high arctic could add still more methane and nitrous oxide to the atmosphere. The combination of the response of wetlands and permafrost may add as much or more methane and nitrous oxide to the atmosphere as expected from the increasing anthropogenic sources. Since adding methane is about 20 times more effective in increasing global temperatures as adding equal amounts of carbon dioxide, and nitrous oxide is perhaps more than 200 times as effective, even small increases in the emissions of these gases could be amplified into large effects on the earth's temperature and climate. The global warming that has apparently occurred over the past century may already have produced about 20% of the increase of nitrous oxide between the pre-industrial times and the present. DOI: 10.1111/j.1600-0889.1989.tb00141.x
83 citations
TL;DR: In this article, the authors examined the spatial variability of methane flux within a large regional wetland system, the Florida Everglades, and investigated the association of flux variability with relevant surface characteristics such as soil thickness, water depth, soil temperature, and vegetative community distribution.
Abstract: Natural wetlands are presumed to be major sources of atmospheric methane, but current estimates of the global wetland emission vary by almost a factor of 20. Estimates of global source strengths are based on extrapolation of in situ flux measurements to large areas occupied by broad classes of wetland environments, and recent efforts at refinement of these estimates have concentrated on improving inventories of the global distribution of major wetland types. An additional potential source of uncertainty which has not been quantified is regional scale variability in emission rates within the major wetland types. We conducted an experiment which examined the spatial variability of methane flux within a large regional wetland system, the Florida Everglades. We also investigated the association of flux variability with relevant surface characteristics such as soil thickness, water depth, soil temperature, and vegetative community distribution. Unit area methane flux to the atmosphere from water-saturated Everglades environments, measured in situ, varied over more than an order of magnitude (4.2 to 81.9 mg CH4/m2/d), depending on which habitat component of the ecosystem was sampled. Observed physical characteristics of the surface (water and soil depth, soil temperature) were not quantitatively associated with the variability in flux rates. However, the distribution of vegetative community types provided an empirical indicator of flux, permitting an inventory of emissions to be based on mapping of regional vegetation patterns. Use of high-resolution, orbital remote sensing data helped reduce uncertainty in the emission inventory of the Everglades by directing in situ sampling efforts to important habitat types and by providing a means for calculating area-weighted mean flux for the system as a whole. The results indicated that spatial variability in flux within a major wetland ecosystem can introduce significant uncertainty in extrapolations to larger areas, even if the extent of the major ecosystem itself is well known. The results also suggested that the response of total ecosystem flux to changing water level is not a linear function of flooded area, but is damped, with regional flux at lowered water levels decreasing proportionally less than flooded area. Both sources of variability can be addressed by the combination of remote sensing and in situ techniques we have employed in the Everglades.
80 citations
TL;DR: In the Arctic, methane gas hydrates represent a significant source of methane, which may become more important if Arctic warming occurs as part of global climate change as discussed by the authors, and the danger of a thermal runway caused by CH4 release from permafrost is minor, but real.
Abstract: Northern sources, including wetlands and perhaps gas hydrates, contribute significantly to the CH4 content of the atmosphere. Methane production from northern wetlands, including bogs, swamps, and ponds, is probably very seasonal, being most important in late summer, with significant evasion in autumn as lakes overturn. The strong recovery of beaver populations in Canada, from near-extinction 50 years ago to present abundance, may also be important, both in creating new wetlands and in the alteration of them; wetlands that have been altered by beaver activity produce orders of magnitude more methane than beaver-free wetlands. In the Arctic, methane gas hydrates represent a significant source of methane, which may become more important if Arctic warming occurs as part of global climate change. The danger of a thermal runway caused by CH4 release from permafrost is minor, but real. Other high-latitude sources of CH4 include Arctic peat bogs, and losses from natural gas production, especially in the Soviet U...
69 citations
TL;DR: In this article, a brief discussion of the measured values of the KIE for these reactions and their application to interpretation of the atmospheric cycles of CO and CH4 is presented, as well as their application in the analysis of the isotopic studies of the two atmospheric trace gases.
Abstract: Kinetic isotopic fractionation plays an important role in the quantitative analysis by isotopic studies of the cycles of the two atmospheric trace gases, CO and CH4, which are important because of their impact on the environment. These gases are scavenged from the atmosphere mainly by homogeneous gas phase oxidation reactions with OH radicals. The isotopic composition of these gases provides constraints on the relative distribution of the fluxes from sources, natural or anthropogenic, of different isotopic compositions. The relationship between the composition of the gas in the atmosphere and the average value of the sources is determined by the fractionation effect of the scavenging processes, in particular the reaction with OH. Thus, knowledge of the fractionation effect is essential to determining the relative distribution of the fluxes from isotopically different sources. The reactions CO + OH and CH4 + OH exhibit several types of KIE’s including normal, inverse, and compound effects resulting from the bimodal character of the former. A brief discussion of the measured values of the KIE for these reactions and their application to interpretation of the atmospheric cycles of CO and CH4 is presented.
50 citations
TL;DR: In this paper, the authors found 188 measurements between 1962 and 1979 reported in various publications with data in 70 of the 216 months, and analyzed these measurements to estimate the trends of methane between 1960 and 1980.
Abstract: Sporadic measurements of atmospheric methane, using gas chromatography, have been taken since the early 1960s. We found 188 measurements between 1962 and 1979 reported in various publications with data in 70 of the 216 months. We have analyzed these measurements to estimate the trends of methane between 1960 and 1980. The data were adjusted for differences of absolute calibration and for latitudinal variations, and analyzed by oridinary regression analysis, weighted regression analysis, and nonparametric methods. Our best estimate of the increasing trend during this period is 13{plus minus}3 ppbv/yr which is similar to, but somewhat less than, the trend of about 17 ppbv/yr over the last decade. {copyright} American Geophysical Union 1989
01 Jan 1989
TL;DR: In the troposphere, methane oxidation leads to sources of O3, CO, and H2 and regulates the concentration of OH radicals (Chameides et al. 1977; Sze 1977; Logan et al 1981) as discussed by the authors.
Abstract: Methane is an important gaseous species in both tropospheric and stratospheric chemistry (see, e.g., Wofsy 1976). In the troposphere, methane oxidation leads to sources of O3, CO, and H2 and regulates the concentration of OH radicals (Chameides et al. 1977; Sze 1977; Logan et al. 1981). In the stratosphere, it is a major source of CH2O and H2 and of upper stratospheric H2O and is the primary sink for CI atoms which take part in ozone-destroying chain mechanisms. Its contribution to global warming, in company with fluorocarbons and nitrous oxides, is second only to that of carbon dioxide (Donner and Ramanathan 1980; Ramanathan et al. 1985).
TL;DR: In order to obtain the distribution and variation of atmospheric CH4 in Japan, measurement of CH4 was performed from June 1985 to March 1988 as mentioned in this paper, and the results showed that CH4 mixing ratios at Tsukuba were 1.768 ppm in 1986 and 1.781 ppm in 1987.
01 Jan 1989
16 Jun 1989
TL;DR: In the atmosphere, certain trace gases both promote global warming and deplete the ozone layer as discussed by the authors, which is the primary radiatively active trace gases that affect global warming are carbon dioxide, nitrous oxide, chlorofluorocarbons, methane, and tropospheric ozone.
Abstract: In the atmosphere, certain trace gases both promote global warming and deplete the ozone layer. The primary radiatively active trace gases that affect global warming are carbon dioxide, nitrous oxide, chlorofluorocarbons, methane, and tropospheric ozone. In the troposphere, the atmosphere up to 10 miles above the earth's surface, these compounds function as greenhouse gases. Many of these gases also influence the concentration of ozone in the stratosphere, the atmospheric layer located between 10-30 miles above the earth's surface. The diffuse layer of ozone in the stratosphere protects life on earth from harmful solar radiation. A reduction of the layer could have very important impacts on the earth's systems. Interactions exist in various ecological processes as well. Physical, chemical, and biological activities of plants and animals are affected directly by global climate change and by increased ultraviolet radiation resulting from depletion of stratospheric ozone.