New research published in Global Biogeochemical Cycles, a journal of the American Geophysical Union, reveals that recent rises in the atmospheric methane levels are probably driven by biological sources, such as cow burps, rice fields, or swamp gas, rather than emissions from fossil fuels.
Atmospheric methane, a major greenhouse gas, traps heat in the atmosphere and contributes to global warming. Methane levels in the atmosphere have been rising by a considerable amount since 2007, and in 2014 the growth rate doubled previous years. This was largely due to biological sources, opposed to fossil fuel emissions.
Conventional Wisdom Refuted
The research, led by scientists at Royal Holloway, University of London, reveals that methane emissions have been rising, mostly in the tropics. Scientist found that biological sources like methane emissions from swamps account for 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. Our analysis of methane’s isotopic composition clearly points to increased emissions from microbial sources, such as wetlands or agriculture.
Euan Nisbet, University of London
Methane Growth Rate Doubles
Professor Nisbet says “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.”
He continued, “At the beginning of this century it appeared that the amount of methane in the air was stabilising, but since 2007 the levels of methane have started growing again. The year 2014 was extreme, with the growth rate doubling, and large increases seen across the globe.”
Tropics Identified as Key Source
In recent years, the rise in methane has been mainly driven by sharp rises in the tropics, due to the changes in weather patterns. It could be possible that the natural processes used to eliminate methane from the atmosphere have slowed, however, there has been an increase in methane emission, particularly from the hot wet tropics.
Professor Nisbet and his collaborators, along with the US The National Oceanic and Atmospheric Administration (NOAA), have been examining samples as well as measurements of air taken from different places like Ascension, a UK territory in the South Atlantic; Cape Point in South Africa; and Alert in the Canadian Arctic.
International Collaboration Leads to New Conclusions
An international team of atmospheric researchers, led by Euan Nisbet from Royal Holloway, University of London, carried out the research. Ed Dlugokencky, from the NOAA, Martin Manning from Victoria University, Wellington, New Zealand and a team from the University of Colorado’s Institute of Arctic and Alpine Research, headed by Jim White, have been working with collaborators from the UK, South Africa, Canada, and France.