Atmospheric methane

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

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.

Past Climate Variability in South America and Surrounding Regions: From the Last Glacial Maximum to the Holocene

Abstract: derstand permafrost dynamics and the relationship with atmospheric methane concentrations over longer timescales. It is clear from paleorecords that peatland permafrost has expanded and contracted over the Holocene at differenttimes in differentplaces (e.g., Vardy et al., 2005; Oksanen, 2006). Although the impacts of Holocene peatland expansion on atmo-spheric methane are now being explored (Smith et al., 2004; Korhola et al., 2010; Beilman et al., this issue), the implications of Holocene permafrost variability on past global methane concentrations have not yet been assessed. The sparse data on contemporary methane emissions show that peatlands with and without perma-frost differsignificantly in their function-ing. More continuous measurements are required to document ongoing changes. Modern process models of carbon dy-namics linked to paleoreconstructions of permafrost could produce critical insights into Walter, K.M., Edwards, M.E., Grosse, G., Zimov, S.A. and Chapin, F.S., long-term role and functioning of northern peatlands in the global carbon cycle.

Methane Dynamics of Aquaculture Shrimp Ponds in Two Subtropical Estuaries, Southeast China: Dissolved Concentration, Net Sediment Release, and Water Oxidation

Abstract: Aquaculture ponds are potentially large sources of atmospheric methane (CH4) that can exacerbate climate change. A thorough understanding of various CH4 biogeochemical processes occurring in the ponds is essential for the prediction and management of CH4 emissions arising from aquaculture. However, the variations in pond CH4 biogeochemical processes among estuaries and aquaculture stages remain poorly understood. In this study, we assessed the net sediment release, oxidation, and dissolved concentrations of CH4 in aquaculture ponds in two subtropical estuaries among three shrimp growth stages. Overall, porewater CH4 concentrations and sediment CH4 release rates varied greatly among different stages in the order: middle stage > final stage > initial stage. Water column CH4 concentrations and overlying water CH4 oxidation rates showed an increasing trend over the study period. Sediment CH4 release rates and dissolved CH4 concentrations also varied considerably between the two estuaries. In the more saline Jiulong River Estuary, sediment CH4 release rate was lower while the shrimp survival rate and yield were higher as compared to the Min River Estuary with a lower water salinity. Our results suggest that both high water salinity and feed utilization efficiency can effectively mitigate CH4 emissions from the coastal shrimp ponds. Overall, the large magnitude of net CH4 emissions observed in our shrimp ponds highlights the urgency of formulating appropriate policies and building sustainable institutions that can strike a balance between land‐based aquaculture development and greenhouse gas mitigation in the subtropical coastal regions.