27 September 2016
by Sarah Honeycombe
Research published today in Global Biogeochemical Cycles, a journal of the American Geophysical Union, shows recent rises in methane levels in the atmosphere are most likely driven by biological sources, such as swamp gas, cow burps, or rice fields, rather than fossil fuel emissions.
Atmospheric methane is a major greenhouse gas that traps heat in our atmosphere, contributing to global warming. Methane levels have been growing strongly since 2007, and in 2014 the growth rate of methane in the atmosphere was double that of previous years.
The study, led by researchers at Royal Holloway, University of London shows methane emissions have been increasing, particularly in the tropics. The study authors discovered biological sources, such as methane emissions from swamps, make up the majority of the increase.
“Our results go against conventional thinking that the recent increase in atmospheric methane must be caused by increased emissions from natural gas, oil, and coal production,” said Euan Nisbet, an atmospheric scientist at Royal Holloway, University of London and lead author of the new study. “Our analysis of methane’s isotopic composition clearly points to increased emissions from microbial sources, such as wetlands or agriculture.”
Atmospheric methane is one of the most potent greenhouses gases. Methane increased through most of the 20th century, driven largely by leaks from the gas and coal industries. At the beginning of this century, it appeared the amount of methane in the air was stabilizing, but since 2007 levels of methane have started growing again. 2014 was extreme, with the growth rate doubling, and large increases seen across the globe, according to Nisbet.
The new sudy shows that in recent years, the increase in methane has been driven by sharp increases in the tropics, in response to changing weather patterns. It is possible the natural processes that remove methane from the atmosphere have slowed down, but it is more likely that there’s been an increase of methane emission instead, especially from the hot wet tropics, according to the authors.
Nisbet and his team, together with NOAA, have been looking at methane measurements and samples of air taken from places like the Canadian Arctic, Ascension, a UK territory in the South Atlantic, and Cape Point, South Africa.
—Sarah Honeycombe is a public relations officer at Royal Holloway, University of London. This post originally appeared as a press release on the Royal Holloway website.