California Institute of Technology. “Natural-gas leaks are important source of greenhouse gas emissions in Los Angeles.” ScienceDaily. ScienceDaily, 12 August 2019. <www.sciencedaily.com/releases/2019/08/190812144922.htm>
Scientist have found that methane in L.A.’s air correlates with the seasonal use of gas for heating homes and businesses. In discussions of anthropogenic climate change, carbon dioxide generally gets the spotlight, but it is not the only greenhouse gas spewed into the atmosphere by human activity, nor is it the most potent.
Methane is another greenhouse gas that is increasing in Earth’s atmosphere because of humans. Methane is produced by human activity in much smaller amounts than carbon dioxide, but it is roughly 25 times more powerful as a greenhouse gas. Though it is often associated with cow flatulence, bovines are not the only human-associated source of methane.
New research by Caltech scientists shows that, at least in the Los Angeles Basin, leaks of natural gas used for heating homes and businesses are major contributors to methane in the atmosphere.
The research was conducted by Liyin He (MS ’18), a graduate student in environmental science and engineering, while working in the lab of Yuk L. Yung, Caltech professor of planetary science and research scientist at the Jet Propulsion Laboratory, which Caltech manages for NASA. She found that methane concentrations in the air above L.A. fluctuate in tandem with the seasons. In winter, when natural gas use is at its highest, methane concentrations are also highest. In the summer, when natural gas use drops, so does the amount of methane in the air.
“Naturally, methane emissions should be pretty flat across the seasons, but maybe a little higher in the summer period because of a lot of things decompose from higher temperatures,” He says. “But it seems that in the city, natural gas consumption is so high in the winter that a lot of it leaks into the atmosphere.”
He conducted her research by using a device called a remote-sensing spectrometer atop Mt. Wilson, a mountain whose peak towers a mile above Los Angeles. From its lofty perch, the spectrometer had a view of a wide swath of the urban area below. Methane is invisible to human eyes, but it is easily seen by the spectrometer because it strongly absorbs infrared light, the wavelength of light to which the spectrometer is sensitive.
Using this setup, the spectrometer was pointed at 33 surface sites around the region and collected methane measurements six to eight times a day for six years. When those measurements were aggregated, a clear pattern emerged: methane levels in the atmosphere peaked each December and January and dipped to a low each June and July.
Though He’s research does not identify specific sources of methane, she says that it is likely that the entire natural gas distribution system, from storage fields to pipelines to stoves and furnaces, is responsible for the leaks.
Because methane is such a potent greenhouse gas, and because it is relatively short-lived in the atmosphere, identifying and reducing those natural gas leaks is one way humans might help reduce the effects of climate change, He says.
“Agriculture and wetlands are still the most important sources of methane when we consider the global scale, He says. “But I think pipeline leakage is the most important one when it comes to cities.”
Liyin He, Zhao‐Cheng Zeng, Thomas J. Pongetti, Clare Wong, Jianming Liang, Kevin R. Gurney, Sally Newman, Vineet Yadav, Kristal Verhulst, Charles E. Miller, Riley Duren, Christian Frankenberg, Paul O. Wennberg, Run‐Lie Shia, Yuk L. Yung, Stanley P. Sander. Atmospheric Methane Emissions Correlate With Natural Gas Consumption From Residential and Commercial Sectors in Los Angeles. Geophysical Research Letters, 2019; DOI: 10.1029/2019GL083400
California Institute of Technology. “Natural-gas leaks are important source of greenhouse gas emissions in Los Angeles.” ScienceDaily. ScienceDaily, 12 August 2019. <www.sciencedaily.com/releases/2019/08/190812144922.htm>.
As methane concentrations increase in the Earth’s atmosphere, chemical fingerprints point to a probable source: shale oil and gas, according to new Cornell University research published today (14 August) in Biogeosciences, a journal of the European Geosciences Union.
The research suggests that this methane has less carbon-13 relative to carbon-12 (denoting the weight of the carbon atom at the centre of the methane molecule) than does methane from conventional natural gas and other fossil fuels such as coal.
This carbon-13 signature means that since the use of high-volume hydraulic fracturing — commonly called fracking — shale gas has increased in its share of global natural gas production and has released more methane into the atmosphere, according to the paper’s author, Robert Howarth, the David R. Atkinson Professor of Ecology and Environmental Biology at Cornell University in the US.
About two-thirds of all new gas production over the last decade has been shale gas produced in the United States and Canada, he said.
While atmospheric methane concentrations have been rising since 2008, the carbon composition of the methane has also changed. Methane from biological sources such as cows and wetlands have a low carbon-13 content — compared to methane from most fossil fuels. Previous studies erroneously concluded that biological sources are the cause of the rising methane, Howarth said.
Carbon dioxide and methane are critical greenhouse gases, but they behave quite differently in the atmosphere. Carbon dioxide emitted today will influence the climate for centuries to come, as the climate responds slowly to decreasing amounts of the gas.
Unlike its slow response to carbon dioxide, the atmosphere responds quickly to changes in methane emissions. “Reducing methane now can provide an instant way to slow global warming and meet the United Nations’ target of keeping the planet well below a 2-degree Celsius average rise,” Howarth said, referring to the 2015 Paris Agreement that boosts the global response to climate change threats.
Atmospheric methane levels had previously risen during the last two decades of the 20th century but levelled in the first decade of 21st century. Then, atmospheric methane levels increased dramatically from 2008-14, from about 570 teragrams (570 million tons) annually to about 595 teragrams, due to global human-caused methane emissions in the last 11 years.
“This recent increase in methane is massive,” Howarth said. “It’s globally significant. It’s contributed to some of the increase in global warming we’ve seen and shale gas is a major player.”
“If we can stop pouring methane into the atmosphere, it will dissipate,” he said. “It goes away pretty quickly, compared to carbon dioxide. It’s the low-hanging fruit to slow global warming.”
The research published in Biogeosciences was funded by the Park Foundation and the Atkinson Center.
Materials provided by European Geosciences Union. Note: Content may be edited for style and length.
- Robert W. Howarth. Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane? Biogeosciences, 2019 DOI: 10.5194/bg-16-3033-2019
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European Geosciences Union. “Fracking prompts global spike in atmospheric methane, study suggests.” ScienceDaily. ScienceDaily, 14 August 2019. <www.sciencedaily.com/releases/2019/08/190814090610.htm>.