Agriculture overtakes fossil fuels in global methane emissions: New Zealand-led study

Agriculture -- and not fossil fuels -- is the major cause of the rise in methane levels in the atmosphere over the last decade, according to a New Zealand-led study on climate change out Friday.

The study led by the government's National Institute of Water and Atmospheric Research (NIWA) concluded that increasing levels of methane since 2007 were most likely due to agricultural practices, and not fossil fuel production as previously thought.

The amount of methane -- a greenhouse gas and one of the major contributors to climate change -- in the atmosphere is estimated to have risen by about 150 percent since 1750, said study leader and NIWA atmospheric scientist Hinrich Schaefer.

NIWA researchers worked with scientists in Germany and the United States to calculate the global average methane in the atmosphere for each year and look at how it changed over time.

The amount had been steadily increasing since pre-industrial times, but then leveled out for about seven years from 1999, and after 2006 it began to rise again.

"We found we could distinguish three different types of methane emissions," Schaefer said in a statement.

"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 leveling out in methane emissions occurred, economic collapse in the Soviet Union caused oil production to decline dramatically, a factor that could be detected in atmospheric analysis.

However, analysis since 2006 ruled out fossil fuel production as the cause of methane increasing again.

"That was a real surprise, because at that time the U.S. 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 included Southeast Asia, China and India -- regions dominated by rice production and agriculture.

"From that analysis we think the most likely source is agriculture," he said.

"If we want to mitigate climate change, methane is an important gas to deal with. If we want to reduce methane levels, this research shows us that the big process we have to look at is agriculture."

The situation could lead to a vicious cycle of global warming as wetlands produced more methane if there was more rain and if it was warmer, while thawing permafrost produced methane and methane was also found in ice-like structures in ocean sediments.

"Which means that global warming could result in more methane being produced from these natural sources. You could have a situation where humans are causing global warming, which causes natural methane sources to emit more methane, contributing to further warming," said Schaefer.

"We don't see that, maybe not yet. Our findings at least give us an angle to tackle the problem."

Schaefer also warned it would be wrong to conclude that the study gives fossil fuel a clean bill: "If fossil fuel production picks up again, that may change the situation dramatically." Endit