Global Ethane Concentrations Rising Again, Says Study

Steady decline of ethane emissions following peak in 1970s ended between 2005-2010

Global emissions of ethane, an air pollutant and greenhouse gas, are on the uptick again, according to a new study led by the University of Colorado Boulder.

The team found that a steady decline of global ethane emissions following a peak in about 1970 ended between 2005 and 2010 in most of the Northern Hemisphere and has since reversed, said CU-Boulder Associate Research Professor Detlev Helmig, lead study author.  Between 2009 and 2014, ethane emissions in the Northern Hemisphere increased by about 400,000 tons annually, the bulk of it from North American oil and gas activity, he said.

The decline of ethane and other non-methane hydrocarbons (NMHC) starting around 1970 is believed to be primarily due to better emission controls, said Helmig.  The controls resulted in reduced emissions from oil and gas production, storage and distribution, as well as combustion exhaust from cars and trucks.

"About 60 percent of the drop we saw in ethane levels over the past 40 years has already been made up in the past five years," said Helmig.  "If this rate continues, we are on track to return to the maximum ethane levels we saw in the 1970s in only about three more years.  We rarely see changes in atmospheric gases that quickly or dramatically."
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The study also showed that among the air sampling locations around the world, the largest increases in ethane and shorter-lived propane were seen over the central and eastern United States, areas of heavy oil and gas activity, said Helmig.

"We concluded that added emissions from U.S. oil and gas drilling have been the primary source for the atmospheric ethane trend reversal," he said.

The study, published in Nature Geoscience, also indicated that emissions of total NMHC in the Northern Hemisphere are now increasing by roughly 1.2 million tons annually.

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