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Global Climate Change DigestArchives of the
Global Climate Change Digest

A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999

FROM VOLUME 11, NUMBER 7, JULY 1998

PROFESSIONAL PUBLICATIONS...
METHANE CYCLE


Item #d98jul62

"Long-Term Growth at Elevated Carbon Dioxide Stimulates Methane Emission in Tropical Paddy Rice," (see Impacts of Elevated CO2, this Global Climate Change Digest issue--July 1998).


Item #d98jul63

"Global Methane Emission from Wetlands and Its Sensitivity to Climate Change," M. Cao, K. Gregson, S. Marshall (Biolog. Sci., Univ. Nottingham, Loughborough LE12 5RD, UK; e-mail: Stewart.Marshall@Nottingham.ac.uk),Atmos. Environ., 32(19), 3293-3299, Oct. 1998.

Uses process-based ecosystem models to estimate a global emission of 145 Tg/year, of which 92 Tg/year comes from natural wetlands and 53 Tg/year from rice paddies. Emissions from high-latitude wetlands and rice paddies were only half those reported in the traditional literature, confirming more recent measurements. The models show that modest global warming may produce a higher emission, but this effect may be reversed by larger increases in temperature, because of soil moisture depletion.


Item #d98jul64

"Atmospheric Methane Between 1000 A.D. and Present: Evidence of Anthropogenic Emissions and Climatic Variability," D.M. Etheridge (Atmos. Res., CSIRO, PMB 1, Aspendale, Victoria 3195, Australia; e-mail: dme@dar.csiro.au), L.P. Steele et al.,J. Geophys. Res., 103(D13), 15,979-15,993, July 20, 1998.

Unifies and coordinates several records of methane including those from ice cores. Calculates an average total methane source of 250 Tg/year for 1000-1800 A.D., reaching near stabilization at about 560 Tg/year in the 1980s and 1990s. The calculated trend of methane and one of its isotopes supports the stabilization of the total methane source.


Item #d98jul65

"Continuing Decline in the Growth Rate of the Atmospheric Methane Burden," (see Of General Interest, this Global Climate Change Digest issue--July 1998).


Item #d98jul66

"Changing Concentration, Lifetime and climate Forcing of Atmospheric Methane," J. Lelieveld (Inst. Marine & Atmos. Res., Princetonplein 5, 3584 CC Utrecht, Neth.), P.J. Crutzen, F.J. Dentener,Tellus, 50B(2), 128-150, Apr. 1998.

Reviews source and sink estimates and presents global 3D model calculations, showing that the main features of the global methane distribution are well represented. Scenario calculations indicate that the importance of the climatic forcing of methane relative to that of CO2 will decrease from about 35% now to about 15% in the year 2050.


Item #d98jul67

"Methane Fluxes on Boreal Peatlands of Different Fertility and the Effect of Long-Term Experimental Lowering of the Water Table on Flux Rates," H. Nykanen (Natl. Public Health Inst., POB 95, FIN-70701 Kuopio, Finland; e-mail: Hannu.Nykanen@ktl.fi), J. Alm et al.,Global Biogeochem. Cycles, 12(1), 53-69, Mar. 1998.

Methane fluxes were measured at 17 peatland sites with different nutritional and hydrological characteristics by a static chamber technique. Results can be used to predict the possible changes in methane emissions if climate is drying in the north. For instance, lowering the present water table by 10 cm would induce a 70% reduction in emissions from fens and a 45% reduction from bogs.


Item #d98jul68

"Response of Tundra CH4 and CO2 Flux to Manipulation of Temperature and Vegetation," J.H. Verville (Dept. Biolog. Sci., Stanford Univ., Stanford CA 94305), S.E. Hobbie et al., Biogeochemistry, 41, 215-235, 1998.

Conducted removals of plant species, air temperature manipulations, and vegetation and soil transplants in Alaskan wet-meadow and tussock tundra communities. Results strongly suggest that changes in methane and CO2 flux in response to climate change will be more strongly mediated by large-scale changes in vegetation and soil parameters than by direct temperature effects.


Item #d98jul69

"Sensitivity of the Atmospheric CH4 Growth Rate to Global Temperature Changes Observed from 1980 to 1992," S. Bekki (Ctr. Atmos. Sci., Univ. Cambridge, Lensfield Rd., Cambridge CB2 1EW, UK), K.S. Law, Tellus, 49B(4), 409-416, Sep. 1997.

Uses a 2-D chemistry-transport model to explore two competing temperature dependencies of methane: emissions from wetlands, and destruction related to OH concentration. The wetland effect dominates in the Northern Hemisphere; the OH effect is more important in the tropics.


Item #d98jul70

"North Siberian Lakes: A Methane Source Fueled by Pleistocene Carbon," S.A. Zimov...F.S. Chapin III (Dept. Integrative Biol., Univ. California, Berkeley CA 94720) et al.,Science, 277(5327), 800-802, Aug. 8, 1997.

Estimates that emissions from north Siberian lakes contributes about 1.5 teragrams of methane per year to observed winter increases in atmospheric methane concentrations.


Item #d98jul71

"Enhanced CH4 Emissions from a Wetland Soil Exposed to Elevated CO2," J.P. Megonigal (Dept. Biol., George Mason Univ., Fairfax VA 22030), W.H. Schlesinger, Biogeochemistry, 37(1) 77-88, Apr. 1997.

Glasshouse and growth chamber experiments show that elevated CO2 may dramatically increase methane emissions from wetlands, a source that currently accounts for 40% of global emissions.


Item #d98jul72

"An Inverse Modeling Approach to Investigate the Global Atmospheric Methane Cycle," R. Hein (Inst. Physik Atmos., DLR Oberpfaffenhofen, D-82234 Wessling, Ger.), P.J. Crutzen, M. Heimann,Global Biogeochem. Cycles, 11(1), 43-76, Mar. 1997.

Deduces information on methane sources and sinks from observed spatial and temporal variations of atmospheric methane mixing ratios, using a 3-D atmospheric transport model combined with a tropospheric chemistry module. Constructs two scenarios which reproduce the main features seen in the NOAA/CMDL methane observations for the 1980s. Examines the decrease in growth rate in the early 1990s, which cannot be associated uniquely with any particular source.


Item #d98jul73

Two related items in Nature, 385(6615), Jan. 30, 1997:

"Bottom Line for Hydrocarbons," I.R. MacDonald (College of Geosci., Texas A&M Univ., College Sta. TX 77843), 389-390. There is renewed scientific interest in oceanic methane gas hydrates—a solid form of methane combined with water—because they play a potentially enormous role in the global carbon cycle. The following paper revises upwards the world stores of gas hydrates.

"Direct Measurement of in situ Methane Quantities in a Large Gas-Hydrate Reservoir," G.R. Dickens (Dept. Earth Sci., James Cook Univ., Townsville, Queensland 4811, Australia), C.K. Paull et al., 426-428. Reports direct measurements of methane stored as gas hydrate and free gas in a sediment from the western Atlantic Ocean. Results indicate substantial quantities of methane stored as gas hydrate, with an equivalent or greater amount occurring as bubbles of free gas in the sediments below the hydrate zone.


Item #d98jul74

"Is the Amplitude of the Methane Seasonal Cycle Changing?" E.J. Dlugokencky (NOAA/CMDL, 325 S. Broadway, Boulder CO 80303; e-mail: edlug@cmdl.noaa.gov), K.A. Masarie et al.,Atmos. Environ., 31(1), 21-26, Jan. 1997.

Analyzes 12 years of data from a globally distributed set of sampling sites. If there are systematic changes occurring in the seasonal cycle of atmospheric methane, a longer record will be needed to extract them from measurements.


Item #d98jul75

"Atmospheric Methane over the Last Century," M.A.K. Khalil (Dept. Physics, Portland State Univ., POB 751, Portland OR 97207), M.J. Shearer, R.A. Rasmussen,World Resource Review, 8(4), 481-492, Dec. 1996.

Reviews the role of methane in the environment and how well we understand the trends over the last 100 years, particularly possible reasons for the recent slowdown in the global rate of increase of methane in the atmosphere.


Item #d98jul76

"Changing Trends in Tropospheric Methane and Carbon Monoxide: A Sensitivity Analysis of the OH Radical," H. van Dop (Inst. Marine & Atmos. Res.-IMAU, Utrecht Univ., POB 80005, 3508 TA Utrecht, Neth.; e-mail: dop@fys.ruu.nl), M. Krol,J. Atmos. Chem., 25(3), 271-288, Nov. 1996.

Concludes that climatic fluctuations (tropospheric water vapor, temperature and convective activity) and stratospheric ozone depletion (through tropospheric UV radiation) have a significant influence on tropospheric composition, and thus on trends in methane and carbon monoxide concentrations.


Item #d98jul77

"Nitrous Oxide and Methane fluxes from Perturbed and Unperturbed Boreal Forest Sites in Northern Ontario," (see Nitrogen Cycle, this Global Climate Change Digest issue--July 1998).


Item #d98jul78

"Changes in CH4 and CO Growth Rates after the Eruption of Mt. Pinatubo and Their Link with Changes in Tropical Tropospheric UV Flux," E.J. Dlugokencky (NOAA/CMDL, 325 S. Broadway, Boulder CO 80303; e-mail: edlug@cmdl.noaa.gov), E.G. Dutton et al., Geophys. Res. Lett., 23(20), 2761-2764, Oct. 1, 1996.

Trace gas measurements and calculations suggest that decreased UV flux following the Pinatubo eruption decreased the steady-state OH concentration, and led to the observed anomalously large growth rates for methane and CO in the early 1990s.


Item #d98jul79

"Deforestation and Methane Release from Termites in Amazonia," C. Martius (INPA, Caixa Postal 478, 69.011-970 Manaus-Amazonas, Brazil), P.M. Fearnside et al.,Chemosphere, 33(3), 517-536, Aug. 1996.

Re-evaluates and rejects the hypothesis that deforestation leads to higher populations of wood-feeding termites, and to a significant increase in termite-emitted methane, in areas of cleared and burned former primary rain forest.


Item #d98jul80

"A Reevaluation of the Open Ocean Source of Methane to the Atmosphere," T.S. Bates (PMEL, NOAA, 7600 Sand Pt. Way NE, Seattle WA 98115), K.C. Kelly et al.,J. Geophys. Res., 101(D3), 6953-6961, Mar. 20, 1996.

Using seawater and atmospheric methane mixing ratios measured on several cruises in the Pacific, estimates a total global ocean-to-atmosphere flux that is an order of magnitude less than estimated by the IPCC (1994).

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