Sky-high methane mystery closer to being solved, researchers say

Commercial natural gas was likely major factor in late 20th century stabilization, academic, NOAA researchers find

August 22, 2012

Levels of atmospheric methane have puzzled researchers in recent decades, first rising steadily due to human activities, then stabilizing for about decade starting in the mid-1990s before rising again in the last four years.  Now, a new paper by academic researchers and a NOAA scientist identifies one reason for the period of slow-to-no growth: Decreased leakage of natural gas from oil fields.

Reduced leaking and venting of natural gas from oil fields probably accounts for up to 70 percent of the decrease in the growth of atmospheric methane at the end of the 20th century, according to new research published Aug. 23, in the journal Nature.

“We can now say with confidence that, based on our data, the trend is largely a result of changes in fossil fuel use,” said University of California, Irvine chemistry professor Donald Blake, senior author on the paper. NOAA’s Lori Bruhwiler, of the Earth System Research Laboratory, is a co-author.

graph of ethane and methane changes

(Rowland-Blake Group, UC Irvine) The figure shows the long-term decline of the global concentration of atmospheric ethane (blue line), which closely matches the long-term decline of the global growth rate of atmospheric methane (pink line). This association clearly shows that fossil fuel reductions are probably responsible for a significant portion of methane’s long-term decline. This data set represents the longest continuous record of global atmospheric ethane levels.

Methane has 20 times the global warming potential of carbon dioxide, although CO2 is far more abunant in the atmosphere. After decades of increases due to worldwide industrial and agricultural activity, the slowing of the growth in atmospheric methane from the 1980s through 2005 was remarkable. Scientists have long wrestled with the cause.

Blake and his team scrutinized data collected and archived by UCI, NOAA’s Global Monitoring Division (which maintains an international cooperative air sampling network around the globe) and the University of Colorado, to track changes in the planet’s atmosphere. The team found that the trapping and sale of natural gas for use as a fuel source, which sharply reduced the skyward venting and flaring of methane from oil fields, was the major factor contributing to the slowdown in methane growth rates. Methane is the main ingredient in natural gas.

“Methane is a potent greenhouse gas and if we want to understand future climate, we need to better understand methane’s dynamics,”  Bruhwiler said.

Since 2007, levels have started to climb again, adding urgency to the scientific mystery. Recent work done by NOAA and University of Colorado researchers has suggested that the boom in oil and gas drilling over the past 5 years could be leading once again to increased methane leakage to the atmosphere.

For nearly 30 years, successive generations of UCI chemistry students and researchers have filled canisters with air samples at remote locations across the globe. NOAA scientists have been monitoring atmospheric changes since 1967, coordinating an international network of samplers taking weekly samples around the globe and analyzing the contents in Boulder, Colo. The breadth and length of these sampling networks proved invaluable in solving the methane puzzle

“This paper speaks to the importance of scientific insight that only can be gained from decades of meticulous, sustained data recording,” said co-author Mads Sulbaek Andersen, formerly of UCI and now with the Jet Propulsion Laboratory.

The lead author of the study is Isobel Simpson of UCI. Other authors are Simone Meinardi, Nicola Blake and F. Sherwood Rowland (posthumous) of UCI and Detlev Helmig of CU. Funding was provided by NASA and NOAA.

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