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Tuesday, May 28, 2013

Shift to Natural Gas Won't Reduce Greenhouse Gases Enough, Study Says


Touted 50 percent benefit over coal could take this century or longer to achieve

Princeton, N.J. - The ongoing shift from coal to gas in electric power generation in the U.S. is unlikely to provide the 50 percent reduction in greenhouse gas emissions typically attributed to it over the next three to four decades, according to a new report by the science and journalism organization Climate Central.

The organization’s analysis of published studies finds projections that ignore methane leaks in the natural gas system are overly optimistic about the global warming impact of increasing gas use in place of coal.

Climate Central has also created an interactive tool to help understand the relationship between methane leakage and the global warming benefit of shifting from coal to gas in power generation. (To embed our interactive tool on your site, use this iframe code.)

Methane is a greenhouse gas more potent than carbon dioxide (CO2). On a pound-for-pound basis, methane has a global warming potential about 100 times that of CO2 initially, although over 20- or 100-year timeframes this reduces to 72 or 25 times.

Climate Central’s analysis found enormous uncertainty about the rate at which methane leaks from the process of natural gas drilling, processing, transmission, and distribution. Published estimates of methane leak rates range from 1 to 8 percent, with peer-reviewed measurements for individual drilling regions as high as 17 percent. The EPA recently revised its national estimate of methane leak rates downward by one-third (to 1.5 percent from 2.2), although there are significant uncertainties in these figures.

“It is impossible to know with confidence what actual leak rates are at a national scale, with the currently available data,” said Eric Larson PhD, a senior scientist at Climate Central and director of the organization’s energy program.

“But even a relatively low overall methane leak rate of 2 percent may not achieve a 50 percent reduction in greenhouse gas emissions compared to coal in this century because of the greenhouse potency of methane.”

In addition to the rate at which methane leaks from the natural gas system, the climate benefits of switching from coal to natural gas depend heavily on the rate at which coal-generated electricity is replaced by gas-generated electricity and how much time has passed after beginning a switchover from coal to gas.

Natural gas use in the U.S. grew by 25 percent from 2007 to 2012, according to the U.S. Energy Information Administration. Within the power sector, natural gas use grew to 36 percent from 30 percent of all gas use. Shale gas produced by hydraulic fracturing has grown especially rapidly, from close to zero a decade ago to about one-third of all gas today. Continued growth is projected, and shale gas could account for half of all gas in another two decades.

As gas production has grown, electricity generated using gas has also grown, from less than 19 percent of all electricity in 2005 to more than 30 percent in 2012. During the same period coal electricity fell from 50 percent to 37 percent.

“More measured data and better understanding of gas industry practices are needed to guide the nations’ energy choices,” Larson said. “Fortunately, we know how to measure methane leaks, and we could get a handle on the uncertainties relatively quickly with a sufficient commitment of resources.

Headquartered in Princeton, New Jersey, Climate Central is a non-profit research and journalism organization providing authoritative information to help the public and policymakers make sound decisions about climate and energy.
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