SA Forum is an invited essay from experts on topical issues in science and technology.
Compared with coal natural gas emits roughly half the carbon dioxide for each unit of usable energy produced. As a result, the transition in baseload electricity generation underway in the U.S. provides the biggest available opportunity to quickly slash greenhouse gas emissions from power production.
Yet methane venting and leaking from the natural-gas supply chain could reduce or even erase those gains. According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (AR5 WGI), more than one third of current radiative forcing (a measurement of how much additional energy is trapped in Earth’s climate system in the present as compared with preindustrial times) is due to relatively short-lived climate pollutants such as methane, tropospheric ozone, black carbon and hydrofluorocarbons (HFCs); two thirds of this arises directly or indirectly from methane. And about one third of the total radiative forcing we will experience over the next two decades from climate pollutants emitted this year will come from methane (based on emissions data from a number of prominent inventories).
The implications are inescapable: Controlling methane emissions is essential to reducing radiative forcing over the near term.
Approximately one third of U.S. methane emissions come from the oil and gas industry. (Other significant sources include farms and landfills.) Although no one can accurately say how much methane is now leaking from wellheads, processing plants, pipelines and other natural gas facilities, there is a growing body of evidence that the amount is significant.
Recent studies suggest that the break-even point for methane emissions from natural gas development is 2.7 percent of total production; emissions rates higher than that would mean that switching from coal to natural gas would be worse for the climate in the short run. In 2012 the U.S. Environmental Protection Agency estimated the total methane emissions from natural gas supply chain and petroleum sources to be 1.5 percent of U.S. natural gas produced. But that may understate the problem. A 2013 study led by Harvard University scientists found that total U.S. anthropogenic methane emissions in 2008, including industrial and agricultural sources, could be 50 percent higher than EPA estimates. A series of peer-reviewed studies will be published in the coming year, deepening our understanding of methane emissions from various geographies and supply chain segments.
We already know enough to start cutting methane leakage, however. A study released this year by the consulting firm ICF International analyzed 11 methane-reduction techniques for 19 sources of industrial emissions. Some measures, such as shifting to lower-emitting pneumatic valves and requiring routine leak detection and repair, would save the industry money; others would impose manageable costs. Overall, ICF found that using currently available technologies, 40 percent of methane emissions from the natural gas supply chain could be eliminated within five years for less than a penny per thousand cubic feet of gas produced. Others have found similarly low costs.
At both state and federal levels, political support for regulatory controls is building. In February Colorado adopted the first rules in the U.S. that directly control methane emissions. After Gov. John Hickenlooper declared “zero tolerance” for methane emissions, the Environmental Defense Fund and three of Colorado’s largest oil and gas producers—Anadarko Petroleum, Encana and Noble Energy—developed a proposal that shaped the regulations. Under the new rules companies must find and fix leaks and use stronger emission controls for storage tanks, dehydrators and gas vents from wells.
The Colorado rule-making is a model for other states and the nation. Last June Pres. Obama included methane controls in his Climate Action Plan, and in the months since an interagency task force has been examining regulatory options. The Administration announced a "methane strategy" on March 28, a first step toward comprehensive regulation. Whereas local water pollution issues resulting from the use of hydraulic fracturing technologies still remain to be resolved, moving ahead with this federal rule-making on methane leakage is in the interests of both the nation and the global climate system.