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Scientists blame rising methane levels on agriculture

Staff writer |
A breakthrough in understanding about the causes of climate change has been published online in the journal Science.

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The findings of a study initiated by scientists from New Zealand’s National Institute of Water and Atmospheric Research (NIWA), rule out fossil fuel production as the major cause in the rise of methane levels in the atmosphere since 2007.

The research, led by NIWA atmospheric scientist Hinrich Schaefer, has concluded that increasing levels of methane in the atmosphere since 2007 are most likely due to agricultural practices, and not fossil fuel production as previously thought.

The amount of methane in the earth’s atmosphere is estimated to have increased by about 150% since 1750.

NIWA scientists first noticed trends occurring in the data collected at NIWA’s clean air monitoring stations at Baring Head in Wellington and Arrival Heights in Antarctica.

With only Southern Hemisphere data to go on, the scientists began to collaborate with the University of Colorado, in the U.S., and Heidelberg University, in Germany, whose scientists were taking similar measurements in a number of locations across the world.

Between 1999 and 2006 scientists observed a plateau in the amount of methane in the atmosphere. The amount had been steadily increasing since pre-industrial times but then levelled out for about seven years. After 2006 it began to rise again and continues to do so.

Around the time the plateau in methane emissions occurred, economic collapse in the Soviet Union caused oil production to decline dramatically—a factor that could now be detected in atmospheric analysis but is of no great surprise to the scientists.

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

“That was a real surprise, because at that time the U.S. started fracing, and we also know that the economy in Asia picked up again, and coal mining increased. However, that is not reflected in the atmosphere,” Dr. 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 Southeast Asia, China and India—regions that are dominated by rice production and agriculture.

“From that analysis we think the most likely source is agriculture. 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," 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.”

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