Methane mystery solved
Scientists now have an explanation as to why methane emissions increased at a much slower rate in the 1990s than originally projected and why levels of the greenhouse gas in the atmosphere have remained relatively constant since 1999.
Paul Steele from the Australian Commonwe alth Scientific and Industrial Research Organization (CSIRO) and his colleagues used a computer model to track the path of methane (CH4) from the atmosphere back to its earthly sources in order to determine the exact origin based on series of measurements over the last twenty years. The researchers attribute the lower growth rates over the last decade to the more efficient use of natural and mine gases by humans, since better technologies have reduced the losses in gas pipelines and the gas from oil production is no longer simply blown into the atmosphere, but was used to generate energy. Since 1999, however, these emissions have increased again due to the economic growth in Asia and reached their previous high level in 2003.
This plus is masked by a decrease in methane emissions from natural sources such as swamps and bodies of water. Their share has fallen because many wetlands have dried out in recent decades due to drainage, droughts or climate change. Should this proportion increase again in the medium term to the average values of the 1990s - for example through increased release from Siberian moors or through renaturation of corresponding ecosystems - the high growth rates of previous decades should soon be reached again. Overall, the methane content of the atmosphere has tripled since the beginning of industrialization. After carbon dioxide, CH4 is the second most important greenhouse gas.
With their investigations, Steele's team was also able to clarify the annual fluctuations in natural methane emissions. They are mainly due to changing vapors from wet areas. Fires, on the other hand, only play a major role during strong El Niño events such as 1997/98, when large areas of swamp forest in Indonesia burned or at least smoldered for months, emitting CH4.