U.S. methane emissions underestimated, study says
CHARLESTON, W.Va. -- Federal government calculations appear to greatly undercount U.S. emissions of the powerful greenhouse gas methane, according to a significant new study published Monday.
Methane emissions are 50 percent larger than estimated by the federal Environmental Protection Agency, and authors of the new study say their conclusions suggest EPA was wrong when it recently decreased agency methane emissions factors for the natural gas industry.
"What we find is that for many regions of the U.S., and most strikingly the south-central U.S., these emissions are much higher than those in current official inventories," said co-author Anna Michalak, a Stanford University environmental engineer.
Michalak and her colleagues used atmospheric methane observations from across North America in 2007 and 2008 to improve estimates of methane gas emissions from a variety of human sources.
The study found large discrepancies with government estimates in some regions of the United States, particularly in the south-central U.S., where total methane emissions were 2.7 times greater than those reported in most inventories.
Methane emissions from just three states, Texas, Oklahoma and Kansas, account for nearly one-fourth of the nation's discharges, or nearly 4 percent of the total U.S. greenhouse gas budget, the new study said.
The new paper was being published in the prestigious Proceedings of the National Academy of Sciences. Co-authors include researchers from Harvard University, the University of Michigan, the National Oceanic and Atmospheric Administration, and the University of Colorado.
Results of the research will continue a growing debate on all as the Obama administration promotes the use of natural gas -- generally thought to be a cleaner alternative to coal -- as part of a plan to combat potentially devastating impacts of global warming.
The new study found that emissions from oil and gas drilling and processing in the south-central U.S. could account for half of the region's methane emissions, and represent a source almost five times higher than in the most commonly used global emissions databases.
Also, the study found emissions were nearly twice as large as current inventories showed for livestock operations, mostly from animal belching and flatulence, and from manure management.
Burning coal for electricity produces about twice the carbon dioxide as burning natural gas, but some scientists remain concerned about methane emissions that leak from gas-drilling operations, in part because methane is a more potent greenhouse gas than carbon dioxide.
Two years ago, the issue gained much more attention with the publication of a study by a team of Cornell University researchers led by ecology professor Robert Howarth. That study reported that natural gas could be just as bad -- or worse -- than coal for global warming, especially if the issue is examined on the short time frame in which scientists believe action is needed to curb global warming.
Since then, industry officials have harshly criticized Howarth's study, and there's been a lively debate in scientific journals about his results and about the many variables used to estimate methane emissions from the shale-gas boom across the country.
Howarth said the new study is "very compelling and quite important." He called it "the most comprehensive study yet of methane emissions from the United States" and said "the climate change ramifications are immense."
Alisha Johnson, a spokeswoman for the EPA, said agency officials have not yet fully reviewed the new paper, but hope it will "help us refine our estimates going forward."
Steve Everley, a spokesman for EnergyInDepth, a natural gas industry group, questioned the results of the new study because researchers used data that is now five or six years old.
Everley pointed to a September study led by the University of Texas as "the gold standard" for evaluating methane emissions from the boom in natural gas drilling in shale formations around the country.
The UT study, done in conjunction with the Environmental Defense Fund and several gas companies, used a "bottom-up" approach that measured emissions from various parts of the production process at 190 sites around the country. It found slightly lower overall methane emissions from some parts of the process, but higher emissions from others.
The new, "top-down" approach study out this week was based on atmospheric methane levels from nearly 13,000 measurements from airplane flights and telecommunications towers. While the new study's data from 2007 and 2008 could be outdated, it was also gathered right at the beginning of the boom in shale-gas drilling. Authors said the measurements may not contain impact from that boom, and that they are working to renew their analysis with 2012 figures.
Engineer David Allen, lead author of the UT paper published in September, said the new study makes "an important contribution" by using a larger number of measurements to estimate total methane emissions. Allen's study had looked at a subset of emissions sources, to try to identify opportunities for reductions.
"Fossil fuel production and processing and animal husbandry are large and complex activities, with a large number of potential emissions sources," Allen said. "So a logical follow-up question is which sources within these sectors are responsible for the emissions. Some emissions sources may be more important than others."
Scott Miller, a Harvard doctoral student and lead author of the new paper, said, "The bottom-up and top-down approaches give us very different answers about the level of methane gas emissions. It will be important to resolve that discrepancy in order to fully understand the impact of these industries on methane emissions."
Reach Ken Ward Jr. at firstname.lastname@example.org or 304-348-1702.