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Agriculture, Not Fuel, Is Behind Rising Methane

Increasing levels of methane in the atmosphere since 2007 are most likely due to agricultural practices, and not fossil fuel production as previously thought, according to research published in Science (www.tinyurl.com/zmu4wcn).

Methane levels in the atmosphere are estimated to have risen by about 150% since 1750, but levels plateaued between 1999 and 2006. Since then methane levels have been rising again.

Scientists at New Zealand’s National Institute of Water and Atmospheric Research first noticed these trends in the data collected at monitoring stations in Wellington and Antarctica. With only Southern Hemisphere data to go on, the scientists collaborated with American and German researchers who were taking similar measurements in a number of locations across the world.

“We found we could distinguish three different types of methane emissions,” said Dr Hinrich Schaefer. “One is the burning of organic material, such as forest fires. Another is fossil fuel production – the same processes that form natural oil and gas – and the third is formed by microbes which come from a variety of sources such as wetlands, rice paddies and livestock.”

Around the time the plateau in methane emissions occurred, economic collapse in the Soviet Union reduced oil production dramatically, and this could be detected in the atmosphere. However, analysis of the atmosphere since 2006 rules out fossil fuel production as the source of the current rise in methane levels.

“That was a real surprise, because at that time the US started fracking and we also know that the economy in Asia picked up again, and coal mining increased. However, that is not reflected in the atmosphere,” Schaefer said. “Our data indicate that the source of the increase was methane produced by bacteria, of which the most likely sources are natural, such as wetlands or agricultural, for example from rice paddies or livestock.”

Previously published studies had determined that the methane originated from an area that includes South-East Asia, China and India, which are dominated by rice production and agriculture. “From that analysis we think the most likely source is agriculture,” Schaefer said.

“The good news is that if the source was wetlands, we couldn’t do anything about it. But there is ongoing research that is looking at reducing methane production in agricultural practices.”

However, global warming could change this. Wetlands produce more methane if there is more rain and if it’s warmer. Thawing permafrost produces methane, and methane is also found in ice-like structures in ocean sediments. “You could have a situation where humans are causing global warming, which causes natural methane sources to emit more methane, contributing to further warming,” Schaefer said. “We don’t see that, not yet. Our findings at least give us an angle to tackle the problem.”

Schaefer also warned: “If fossil fuel production picks up again that may change the situation dramatically”.