Atmospheric methane

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

Evidence for a link between climate and northern wetland methane emissions

Abstract: Wetlands are an important source of atmospheric methane (CH 4 ), but the strength of this source and its sensitivity to potential changes in climate are still uncertain. In this study, continuous measurements from 1990 to 1998 of atmospheric CH 4 from the Canadian observational sites at Fraserdale (49°53'N 81°34'W) and Alert (82°27'N 62°31'W) are used to estimate CH 4 emissions from the Hudson Bay Lowland (HBL), a 320,000 km 2 semicontinuous wetland region in central Canada. The HBL comprises ∼ 10% of the total area of northern wetlands. A conceptually simple approach was used to calculate the methane emission flux using the CH 4 concentration difference between Alert and Fraserdale, the residence time of the air mass over the HBL, and the mixing height of the convective boundary layer. Emission rates estimated using this approach for 1990 compare well with empirical aircraft and tower flux measurements made within the HBL during the same time period, thus indicating that the methodology used is reasonable. Annual CH 4 emission rates range from 0.23 to 0.50 Tg CH 4 yr -1 and are much lower than many empirical flux measurements observed at other northern wetland sites. A seasonal temperature sensitivity with a Q 10 of about 4 was found. Moreover, the observed interannual variations in emissions are well correlated to variations in annual air temperatures corresponding to a sensitivity of Q 10 7. That is, a 10°C change in annual temperature would result in a sevenfold change in wetland emissions which is much larger than Q 10 values used in current global CH 4 models (typically Q 10 1.5). Our findings suggest that northern wetland emissions are probably overestimated to date but may increase significantly due to predicted global warming.

A model study of the greenhouse effects due to increasing atmospheric CH4, N2O, CF2Cl2, and CFCl3

Abstract: Study of the greenhouse effects of increasing atmospheric trace gases has so far relied mainly on the use of one-dimensional models, especially the radiative-convective models (cf. World Meteorological Organization, 1982; National Research Council, 1983). Here we use the two-dimensional (altitude-latitude) radiative-dynamical model of Wang et al. (1984) to investigate the effects on vertical and meridional temperatures of increases of atmospheric methane, nitrous oxide, and chlorofluorocarbons. The model, consisting of a high-latitude zone and a low-latitude zone, couples the meridional and vertical temperature structure through energy balance between radiative flux and vertical and meridional heat transports. First, we show that the thermal radiation flux perturbations, i.e., the driving force for the subsequent climate change, caused by increases of these trace gases and carbon dioxide, are different in nature. Next, a comparison of model-calculated present climate and climate change between the one-dimensional and two-dimensional models is performed. The results indicate that the two-dimensional model simulates much more realistic temperature and humidity distributions. For a doubling of the atmospheric CO2 concentration of 330 parts per million by volume, the two-dimensional model computes a global surface warming of 3.7 K with larger high-latitude amplification, which is in good agreement with results obtained from general circulation models. For the study of the surface warming due to increases of trace gases, it is found that the one-dimensional model using a 6.5 K km−1 critical lapse rate for convective adjustment appears to calculate a much larger surface warming than the two-dimensional model. On the other hand, the one-dimensional model using the moist adiabatic critical lapse rate, although it can not simulate adequately the present tropospheric temperature structure, calculates surface warming effects in close agreement with those of two-dimensional model results. We have used the two-dimensional model to estimate on the time scale of decades the potential greenhouse effects due to increases of these gases. Although the calculations depend largely on the adopted scenarios for future increases, the results nevertheless reveal that the trace gases could potentially augment the surface warming due to carbon dioxide increase by more than 60%.

Absorption of 3.39-Micron Helium–Neon Laser Emission by Methane in the Atmosphere

Abstract: The paper describes an experiment on the absorption of the 3s2–3p4 helium–neon laser emission at 2947.903 cm−1 (3.39 μ) by methane. The emission frequency coincides closely to one of the components of the P(F+) branch of the ν3 band of methane. Methane and nitrogen in different mixing ratios were introduced into an absorption cell and the transmittance as a function of pressure was determined. By relating the measured absorption coefficient with the known interaction of collision and Doppler effects on the broadening of the absorption line, the separation of the emission line and the nearest absorption line was deduced to be 0.003±0.002 cm−1.The collision broadened full-width at half-maximum of the absorption line was determined to be 0.13±0.04 cm−1 at atmospheric pressure. At 1 atm in the earth’s atmosphere, the transmittance can be calculated to be T=exp(−1.1 L) by using the published value of the concentration of methane where L is the path length in kilometers. The effects of the laser emission in several possible cavity modes and of the several absorption lines in the methane group which overlap each other at high pressures are discussed.

Methane: small molecule, big impact.

Abstract: Methanogenesis occures in anaerobic conditions in vast natural and human made environments. The estimated 1% annual increase in global methane is mainly attributed to human activities. This article gives an overall perspective on methane-producing microbes, which are phylogenetically distinct from all other prokaryotes and eukaryotes, the food chain which produces atmospheric methane, and biochemical pathways leading to methane production in these microbes. 12 refs., 12 figs.