Experimental laboratory studies

The earliest laboratory study reporting an emission of CH4 from leaves was conducted in the late 1950s at the Academy of Sciences of Georgia (Tbilisi) on emissions of volatile organic compounds (VOCs) from leaves of willow and poplar tress (Sanadze and Dolidze, 1960). In that study, mass spectrometric analysis was used to scan the volatile emissions of leaves incubated in 1.5 litre glass containers. Based on their mass spectra they concluded that plants released CH4 as well as ethane, propane,...

The global methane budget

The global CH4 budget is composed of a wide range of sources (see Table 1.1 and also Figure 4.5 in Chapter 4) balanced by a much smaller number of sinks, any imbalance in these sources and sinks resulting in a change in the atmospheric concentration. There are three main sinks for CH4 emitted into the atmosphere, with the destruction of CH4 by hydroxyl (OH) radicals in the troposphere being the dominant one. This process also contributes to the production of peroxy radicals, and it is this that...

Natural sources

Major natural sources include wetlands, termites and release from onshore and offshore geological sources. Recently, living vegetation has also been suggested as an important natural source of CH4. Of the globally significant sources of CH4 to the atmosphere, natural sources are currently outweighed by anthropogenic sources. Together they emit some 582Tg CH4 each year, with 200Tg arising from natural sources (Denman et al, 2007). Given the estimated global CH4 sink of 581Tg per year, the...

The geographical distribution of biomass burning

The locations of biomass burning are varied and include tropical savannas, tropical, temperate and boreal forests, and agricultural lands after the harvest. The burning of fuelwood for domestic use is another source of biomass burning. Global estimates of the annual amounts of biomass burning from these sources are estimated in Table 7.2 (Andreae, 1991). Table 7.2 Global estimates of annual amounts of biomass burning and of the resulting release of carbon to the atmosphere Table 7.2 Global...

Global emission estimates

Global emission estimates for natural geological CH4 sources are listed in Table 4.1 the latest estimates are also summarized in Figure 4.4. Figure 4.4 Estimates of methane emissions from geological sources Source Based on data from Etiope et al (2008) Figure 4.4 Estimates of methane emissions from geological sources Source Based on data from Etiope et al (2008) For global submarine emission estimates, a dual approach was utilized based on the seep flux and on the amount of geological CH4...

Net methane efflux from termites

Termites (worker caste) isolated in the laboratory have been reported to produce CH4 at rates ranging from undetectable levels to 1.6pmol g-1 h-1 (Brauman et al, 1992 Bignell et al, 1997 Nunes et al, 1997 Sugimoto et al, 1998a, 1998b). Zimmerman et al (1982) first drew attention to the potentially large quantities of CH4 emitted by termites. Their estimates were 75-310Tg yr-1, equivalent to 13-56 per cent of global sources. However, subsequent estimates of annual CH4 emissions from termites...