The Methane Module

Methane (CH₄), the most abundant hydrocarbon in the atmosphere, is considered as an important greenhouse gas, second only to carbon dioxide (Ramanathan et al., 1985, Wang and Molnar, 1985). Analysis of air contained in ice cores indicates that the methane concentration has been ca. 0.7 ppm for maybe thousands of years (Khalil and Rasmussen, 1982, and 1987). Around 1700 A.D. the concentration seems to have started increasing slowly to ca. 0.9 ppm around 1900 A.D. Only then did a rapid increase start, probably caused by changes in the sources as well as in the sinks of methane resulting in a present concentration of about 1.7 ppm (Khalil and Rasmussen, 1987). The anthropogenic sources of methane, such as cattle breeding, rice cultivation and the exploitation of fossil fuels have grown over the last centuries, whereas the natural emissions are assumed to have remained unchanged (Khalil and Rasmussen, 1982, and 1985).