Showing papers on "Atmospheric methane published in 1988"

Biogeochemical aspects of atmospheric methane

Abstract: Methane is the most abundant organic chemical in Earth's atmosphere, and its concentration is increasing with time, as a variety of independent measurements have shown. Photochemical reactions oxidize methane in the atmosphere; through these reactions, methane exerts strong influence over the chemistry of the troposphere and the stratosphere and many species including ozone, hydroxyl radicals, and carbon monoxide. Also, through its infrared absorption spectrum, methane is an important greenhouse gas in the climate system. We describe and enumerate key roles and reactions. Then we focus on two kinds of methane production: microbial and thermogenic. Microbial methanogenesis is described, and key organisms and substrates are identified along with their properties and habitats. Microbial methane oxidation limits the release of methane from certain methanogenic areas. Both aerobic and anaerobic oxidation are described here along with methods to measure rates of methane production and oxidation experimentally. Indicators of the origin of methane, including C and H isotopes, are reviewed. We identify and evaluate several constraints on the budget of atmospheric methane, its sources, sinks and residence time. From these constraints and other data on sources and sinks we construct a list of sources and sinks, identities, and sizes. The quasi-steady state (defined in the text) annual source (or sink) totals about 310(±60) × 1012 mol (500(±95) × 1012 g), but there are many remaining uncertainties in source and sink sizes and several types of data that could lead to stronger constraints and revised estimates in the future. It is particularly difficult to identify enough sources of radiocarbon-free methane.

Stable carbon isotopic composition of methane from some natural and anthropogenic sources

Abstract: The results of delta/sup 13/C measurements of several types of major sources of methane are as follows: rice paddies, -67%; the peat bogs of the Lake Agassiz region of northern Minnesota, -67 +- 5%; swamps of the Florida Everglades, -55 +- 3% and biomass burning, -24 to -32%. In addition, results are presented of a study of the delta/sup 13/C of CH/sub 4/ released from a slough, compared to the CH/sub 4/ in the bottom sediment. These isotopic values are used, together with previously published data, to make up a tentative budget of the fluxes of the major sources for atmospheric methane with an averge isotopic composition matching the measured value for atmospheric CH/sub 4/, taking into account the fractionation effect of the sink processes. This budget requires the existence of a significant flux from an anthropogenic source of heavy CH/sub 4/, calculated to be 45 +- 15 Tg yr/sup -1/ if attributed to CH/sub 4/ from biomass burning, with deltaC = -25%. copyright American Geophysical Union 1988

Methane cycling in the sediments of Lake Washington

Abstract: Aerobic oxidation is important in the cycling of methane in the sediments of Lake Washington. About half of the methane flux from depth is oxidized to CO, in the upper 0.7 cm of the sediments and the remainder escapes into the water column. In terms of the total carbon budget of the lake, the upward flux of methane is insignificant with only about 2% of the carbon fixed by primary production being returned as methane. The upward flux of methane, however, does represent about 20% of the organic carbon decomposed within the sediments. In addition, methane oxidation consumes 7-10% of the total oxygen

Methane concentration in the glacial atmosphere was only half that of the preindustrial Holocene

Abstract: Air entrapped in bubbles of cold ice has essentially the same composition as that of the atmosphere at the time of bubble formation. Measurements on ice core samples from Byrd Station (Antarctica) and Dye 3 (Greenland) show that the atmospheric methane concentration was only about 350 parts per 109 by volume (p.p.b.v.) during the last glaciation, compared with a mean preindustrial level of about 650 p.p.b.v. and a present value of 1,650 p.p.b.v.

Potential methane production and methane oxidation rates in peatland ecosystems of the Appalachian Mountains, United States

Abstract: Potential rates of methane production and carbon dioxide production were measured on 11 dates in 1986 in peat from six plant communities typical of moss-dominated peatlands in the Appalachian Mountains. Annual methane production ranged from 2.7 to 17.5 mol/sq m, and annual carbon dioxide production ranged from 30.6 to 79.0 mol/sq m. The wide range in methane production values among the communities found within a single peatland indicates that obtaining one production value for a peatland may not be appropriate. Low temperature constrained the potential for methane production in winter, while the chemical quality of the peat substrate appears to control methane production in the summer. Methane oxidation was measured throughout the peat profile to a depth of 30 cm. Values for methane oxidation ranged from 0.08 to 18.7 microM/hr among the six plant communities. Aerobic methane-oxidizing bacteria probably mediated most of the activity. On a daily basis during the summer, between 11 and 100% of the methane produced is susceptible to oxidation within the peat column. Pools of dissolved methane and dissolved carbon dioxide in pore waters were less than 0.2 and less than 1.0 mol/sq m, respectively, indicating that methane does not accumulate in the pore waters. Peatlandsmore » have been considered as an important source of biologically produced methane. Despite the high rates of methane production, the high rates of methane oxidation dampen the potential emission of methane to the atmosphere. 41 refs., 7 figs., 4 tabs.« less

Methane emission from animals: A Global High-Resolution Data Base

Abstract: We present a high-resolution global data base of animal population densities and associated methane emission. Statistics on animal populations from the Food and Agriculture Organization and other sources have been compiled. Animals were distributed using a 1° resolution data base of countries of the world and a 1° resolution data base of land use. The animals included are cattle and dairy cows, water buffalo, sheep, goats, camels, pigs, horses and caribou. Published estimates of methane production from each type of animal have been applied to the animal populations to yield a global distribution of annual methane emission by animals. There is large spatial variability in the distribution of animal populations and their methane emissions. Emission rates greater than 5000 kg CH4 km−2 yr−1 are found in small regions such as Bangladesh, the Benelux countries, parts of northern India, and New Zealand. Of the global annual emission of 75.8 Tg CH4 for 1984, about 55% is concentrated between 25°N and 55°N, a significant contribution to the observed north-south gradient of atmospheric methane concentration. A magnetic tape of the global data bases is available from the authors.

Isotopic composition of methane released from wetlands: implications for the increase in atmospheric methane

Abstract: Measurements of the delta-C{sup 13} of methane released from tropical, temperate, and arctic wetland sites are reported. The mean delta C{sup 13} values (relative to PDB carbonate standard) for peat bogs and Alaskan tundra are {minus}53 + or{minus}8, {minus}66 + or{minus}5 and {minus}64 + or{minus}5{per thousand}, respectively. These measurements combined with methane flux estimates yield a flux-weighted global average delta-C{sup 13} value of {minus}59 + or{minus}6{per thousand} for methane released from wetlands, a major natural methane source. The agreement between the measured delta-C{sup 13} for methane emitted from wetlands and the calculated steady state value of approximately {minus}6{per thousand} for the delta-C{sup 13} of preindustrial methane sources suggests that methane was predominantly produced biogenically in the preindustrial era. The industrial era time rate of change of the delta-C{sup 13} of the global methane flux is calculated from estimates of the growth rate of the major anthropogenically derived methane sources and the C{sup 13} composition of these sources, and compared to the measured change in the delta-C{sup 13} of methane during the last 300 years. Based on these results, it is estimated that 13 + or{minus}8% of the current global methane flux is derived abiogenically from natural gas and biomass burning,more » whereas the remainder is derived biogenically primarily from wetlands, rice paddies, and livestock. 40 refs., 5 figs., 2 tabs.« less

The Isotopic Composition of Methane in Polar Ice Cores

Abstract: Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that (i) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (ii) that the carbon-13 to carbon-12 ratio of atmospheric CH(4) in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent (13)CH(4) enrichment, although other factors may also contribute.

Radiocarbon determination of atmospheric methane at Baring Head, New Zealand

Abstract: Although methane in the atmosphere is clearly increasing, its sources are still poorly defined. Measurement of carbon isotope ratios allows constraints to be placed on relative source strengths of atmospheric methane because different potential sources have different isotope ratios. Unfortunately, interpreting 13C/12C ratios of atmospheric methane is subject to uncertainty because a correction for isotope fractionation in the oxidation of methane is not well determined. Interpreting 14C/12C ratios is also complicated by the need to correct for release of 14CH4 from nuclear power plants using rough estimates. Simultaneous use of both carbon isotope ratios, however, improves the confidence of interpretation. Here we show that measurements of the 14C/12C ratio, using accelerator mass spectrometry, and 13C/12C ratio of methane from clean Southern Hemisphere air are consistent with current estimates of both types of correction and imply that about 32% of atmospheric methane is derived from fossil carbon sources.

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.

Sources of atmospheric methane in the south Florida environment

Abstract: Direct measurement of methane (CH4) flux from wetland ecosystems of south Florida demonstrates that freshwater wet prairies and inundated sawgrass marsh are the dominant sources of atmospheric CH4 in the region. Fluctuations in soil moisture are an important environmental factor controlling both seasonal and interannual fluctuations in CH4 emissions from undisturbed wetlands. Land use estimates for 1900 and 1973 were used to calculate regional CH4 flux. Human settlement in south Florida has modified wetland sources of CH4, reducing the natural prairies and marsh sources by 37%. During the same period, impoundments and disturbed wetlands were created which produce CH4 at rates approximately 50% higher than the natural wetlands they replaced. Preliminary estimates of urban and ruminant sources of CH4 based on extrapolation from literature data indicate these sources may now contribute approximately 23% of the total regional source. We estimate that the integrated effects of urban and agricultural development in south Florida between 1900 and 1973 resulted in a 26% enhancement in CH4 flux to the troposphere.

Kinetics of Radical Reactions in the Atmospheric Oxidation of CH4

Abstract: today. The recognition that the Earth's atmosphere is being affected by human activity and that a large fraction of the chemistry in the atmosphere is due to free radicals stimulated laboratory studies on �tmospheric free radical reactions in the 1970s and 1980s. Free radical reactions in the oxidation of methane constitute one of the areas that has received a great deal of attention and, consequently, it is better understood than most. I have attempted to review the reactions taking place in the atmospheric oxidation of methane. Methane is the simplest hydrocarbon and the most abundant hydro­ carbon in the Earth's atmosphere. Its concentration is at least a thousand times greater than the next most abundant hydrocarbon. Atmospheric methane concentration has been increasing since the onset of the industrial era (l a,b) and the growth has accelerated in the last two decades (2a,b). The reasons for the increase are not clear. The CH4 flux into the atmosphere may be increasing or its loss rate from the atmosphere may be decreasing. The oxidation of methane generates nearly 30% of the atmospheric CO 1 The US Government has the right to retain a nonexclusive, royalt y-free license in and to any copyright covering this paper.

How has the atmospheric concentration of CO changed

Abstract: Author(s): Cicerone, RJ | Editor(s): Rowland, FS; Isaksen, ISA | Abstract: Carbon monoxide exerts strong control over the chemistry of the troposphere and lower stratosphere through its influence over hydroxyl radical (OH) and ozone concentrations. Thus, CO affects the oxidizing power of the atmosphere and the concentrations of greenhouse gases. Because of its short atmospheric residence time (two or three months) the determination of a secular trend in CO concentrations is very difficult. Temporal increases of CO are expected because certain sources under human control have been growing; these include fossil-fuel usage and increasing atmospheric methane. From the data, it is likely that CO has increased in the Northern Hemisphere in the past 15-30 years. Southern Hemispheric data indicate no positive trend. -from Author

Possible long-term changes in biologically active ultraviolet radiation reaching the ground

Abstract: — Three scenarios for long-term changes in atmospheric ozone over the time period 1960 to 2030 lead to different projections for the ultraviolet radiation flux at the earth's surface Biologically effective fluxes for damage to DNA and generalized damage to plants vary by a factor of 10 or more with latitude and season irrespective of possible changes in ozone The natural latitudinal gradient in radiation corresponds to spatial changes in biologically effective fluxes which are large compared to temporal changes expected from trends in ozone over the time period analyzed In an extreme scenario of ozone change, based on an assumed increase in chlorofluorocarbon release rates of 3% per year after 1980, the annually integrated effective flux for damage to DNA increases by 135% at latitude 40°N between 1960 and 2030 With chlorofluorocarbon release rates held fixed at their 1980 values, the corresponding radiation increase is only 23% In a scenario where atmospheric chlorine remains fixed at its 1960 value, trends in atmospheric methane and nitrous oxide imply a decrease in biologically effective flux at 40°N of 53% between 1960 and 2030

Methane linked to warming

Abstract: 198 Greenhouse effect NATURE VOL. 334 21 JULY 1988 NEWS AND VIEWS Methane linked to warming Ralph J. Cicerone METHANE is an important chemical in the atmosphere; it controls numerous chemi- cal processes and species in the troposphere and stratosphere and its infrared spectrum makes it a strong greenhouse gas. There is compelling evidence that the concentration of methane has increased globally at a rate of about 1 per cent per year since 1978‘ (and probably since the early 1950s2) to about 1.70 parts per million (p.p.m.) in 1988. This rapid contemporary increase began 150-200 years ago, when the concentration was 0.65-0.70 p.p.m. according to analysis of air trapped in dated polar ice cores”. Two new experi- mental studies by Stauffer et a1.“ and Raynaud et a1.’ extend the ice-core record back to 100,000 years before present (BP)q and 161,000 BF’, through the last two major glaciated periods, 18,000 up and 150,000 BP. During glacial maxima, the methane concentration fell to 0.35 p.p.m. whereas during interglacial times it rose to 0.65 p.p.m. , very near modern pre-indus- trial values. Thus, the present concentra- tion and that projected for the future are well above any in charted Earth history. Stauffer et a1.q analysed 24 ice-core samples from Antarctica and Greenland to find the methane pattern during the last glaciation and through the transition to the warmer interglacial. Their Antarctic data extend back to 51,000 31g, the Green- land data back to 100,000 BP. Generally, during the last glaciation, about 20,000 BP, the methane concentration was about 0.35 p.p.m. , increasing to about 0.65 p.p.m. by 14,000 31g. Preceding the last glacial period, it was 0.45-0.50 p.p.m. A similar pattern emerges for the preceding glaciation through analysis of the remarkable Vostok ice core from Antarctica. Raynaud et al.’ extracted methane from 27 core sections from the 155,000-BP glaciated period, the following interglacial (about 130,000 BP) and the intervening transition period. During the glaciation the average methane concen- tration was 0.34 p.p.m., rising to 0.46 p.p.m. during the transition and 0.62 p.p.m. during interglacial times. Clearly, the natural methane background concen- tration during warm times is 0.6-0.7 p.p.m. but is a factor of two lower during glacial epochs. There are even indications from Greenland cores that the concentra- tion was low during a cold subinterval (Younger—Dryas period) of the present interglacial, and relatively high during a warm period of the last glaciation“. One measurement conflicts with this picture; it is the only previous methane concentration published” for a glacial period (27,000 BP), measured as 0.65 p.p.m.. The analytical skill needed for these measurements deserves recognition. Even after a core is obtained and dated successfully, subsequent contamination, the gas-extraction method and chemical, biological or physical factors could all alter the methane content of the trapped gas“. All the indications are that the methane found in the ice cores does truly represent the composition of the atmos- phere on the date of firn closure, when the compacting ice enclosed the gas and became impermeable. Now that we know that the concentration of methane doubled between the lows and interglacial highs, and halved again, we can ask why and use this information to elucidate several components of the 100 years ago ON Thursday, the 12th inst., the anniversary meeting of the Sanitary Institution of Great Britain was held in the theatre of the Royal Institution. The Chairman, Mr, Edwin Chad- wick, in opening the proceedings, claimed credit for the Sanitary Institution of Great Britain and like institutions for a large propor- tion of the reduced death-rate of the metropolis, which was now 14 in 1000. London in that respect compared very favourably with other places, the death-rate in Paris being 27, Vienna 30, and St Petersburg 40. Dr. B. W. Richardson delivered an address on “The Storage of Life as a Sanitary Study.” He began by referring to instances of long life in lower animals and in man. These, he said, by some peculiar process as yet but little investigated, held life as a long profession, and to this faculty he applied the term “The Storage of Life.” The problem which the lecturer placed before the society was stated as follows:— Certain proofs of the power of the human body to lay or store up life to a prolonged period are admitted. What are the conditions which favour such storage, and how can we promote the conditions which lead to it? He stated the conditions in the following order, hereditary qualifications, the virtue of contin- ence, maintenance of balance of bodily functions, perfect temperance, and purity from implanted or acquired diseases. In dealing with all—round temperance, he showed that what- ever quickened the action of the heart beyond its natural speed and force was a stimulant, and in proportion to the unnatural tax inflicted by stimulation there was a reduction in the storage of life. From Nature 38, 276; 19 July 1888. © 1988 Nature Publishing Group Earth’s climate and biogeochemistry. The rate of microbial methanogenesis generally increases with temperature. Also, because the dominant methane sources are on land and not in the oceans“, these sources should be reduced when wetland soils are ice-covered or frozen, sealed off from the atmosphere. Thus our general knowledge of natural sources of methane is consistent with the new ice-core data. But the principal sink of atmospheric methane, reaction with hydroxyl (OH) radicals in the troposphere, should also increase with temperature for two reasons. First, the atmospheric OH concentration generally increases with that of H20, rising with temperature. Second, the rate constant for the reaction of CH, with OH also increases with temperature. But the OH concentration also depends strongly on the amounts of ozone and nitrogen oxide present and the intensity of ultraviolet light. Without a knowledge of these, it is not possible to predict how atmospheric methane des- truction rates respond to temperature perturbations. A warmer Earth with more wetlands would provide more anoxic sites for anaerobic methanogenic bacteria. Overall rates of biological carbon cycling could also be larger. Ice-core CO, data have shown a pattern similar to that of methane”. Both the oxic and anoxic paths of carbon cycling could be slowed during glaciation. The extent to which the de- crease (or increase) of CO, concentration actually causes glaciation (or deglaci- ation) is still debated, but we know now that the greenhouse effects of altered CH, must accompany and add to those of CO, changes. It is dangerous to argue, though, that other indirect effects would ensue. For example, increased CH, need not have led to more tropospheric ozone (another greenhouse gas), as has been proposedl, because in past epochs there may not have been sufficient atmospheric NO, to allow this”. But it is sobering to learn that the methane concentration, like those of carbon dioxide and chlorofluoro- carbons, has already increased to values above those of at least the past 160,000 years and that human activities are clearly involved in these global changes”. El 1. Blake, D.R. & Rowland, F.S. Science 739, 1129-1133 (1988). 2. Rinsland, C.P., Levine, J.S. & Miles, T. Nature 318, 245- 249 (1985). 3. Craig, H. B. & Chou, C. C. Geophys. Res. Left. 9, 1221- 1224 (1982). 4. Rasmussen, R. A. & Khalil, M. A. K]. geophys. Res. 89, 11599-11605 (1984). 5. Stauffer, B., Fischer, G., Neftel, A. & Oeschger, H. Science 229, 1386- I388 (1985). 6. Stauffer. B., Lochbronner, E., Oeschger, H. & Schwander, .l. Nature 332, 812-8l4(l988). 7. Raynaud, D., Chappellaz, 1., Barnola, .l.. Korotkevich, J. S. & Lorius, C. Nature 333, 655-657 (1988). 8. Ehhalt, D. H. Tellur 26, 58-70 (1974). 9. Lorius, C. etal. Nature 316, 591-5960985). 10. Volz, A. & Kley, D. Nature 332, 240-242 (1988). Ralph J. Cicerone is at the National Center of Atmospheric Research, PO Box 3000, Boulder, Colorado 80307, USA.

How the Concentration of Atmospheric CO changed

Abstract: Carbon monoxide exerts strong control over the chemistry of the troposphere and lower stratosphere through its influence over hydroxyl radical (OH) and ozone concentrations. Thus, CO affects the oxidizing power of the atmosphere and the concentrations of greenhouse gases. Because of its short atmospheric residence time (two or three months) the determination of a secular trend in CO concentrations is very difficult. Temporal increases of CO are expected because certain sources under human control have been growing; these include fossil-fuel usage and increasing atmospheric methane. From the data, it is likely that CO has increased in the Northern Hemisphere in the past 15-30 years. Southern Hemispheric data indicate no positive trend. Report of the Dahlem Workshop on the Changing Atmosphere, Berlin, 1987, November 1-6 F. S. Rowland, Ivar S. A. Isaksen, Guy Brasseur. cds. F.S. Rowland and I.S.A. Isakscn. pp. 49-61 John Wilcy a Sons Ltd. © S. Bcrnhard. Dahlcmn...