Methane is one of the more potent greenhouse gases for global warming. In June, 2013, President Obama issued a Climate Action Plan to cut the pollution contributing to climate change. An important part of the strategy involves cutting domestic greenhouse gas emissions. In March, 2014 the Administration issued Strategy to Reduce Methane Emissions, which outlined steps to cut methane emissions. The administration estimates that implementing this strategy could reduce greenhouse gas emissions by up to 90 million tonnes in 2020. The administration expects that this initiative will make an important contribution to meeting the Administration goal of reducing U.S. greenhouse gas emissions in the range of 17 % below 2005 levels by 2020.
Methane warming power
There is disagreement as to just how much more potent methane is than CO2 in warming the atmosphere. The EPA has estimated a factor of 21 times compared to carbon dioxide. But Robert Howarth, an environmental biology professor at Cornell University, has argued that it is actually 72 times as powerful as carbon dioxide in terms of its warming potential.
Methane leaks from oil wells and natural gas wells and systems
In the United States the EPA estimates that emissions of methane directly from human sources were equivalent to approximately 560 million tonnes of carbon dioxide pollution (assuming that methane's warming potential is 21 times that of carbon dioxide) in 2012, representing 9 % of all the greenhouse gases emitted as a result of human activity. Methane emissions are projected to increase to a level equivalent to over 620 million tonnes of carbon dioxide pollution in 2030. The main sources of human-related methane emissions are agriculture (36 percent), natural gas systems (23 percent), landfills (18 percent), coal mining (10 percent), petroleum systems (6 percent), and wastewater treatment (2 percent).
An important area of uncertainty is how much methane is leaking from shale gas and shale oil wells. Howarth has argued that the type of shale gas drilling taking place in Texas, New York and Pennsylvania generates particularly high emissions of methane. A study has estimated that between 3.6% to 7.9% of the methane from shale-gas production escapes to the atmosphere in venting and leaks over the lifetime of a well.
A recent study has used spatial analysis to investigate the spatial distribution of anthropogenic methane sources in the United States by combining comprehensive atmospheric methane observations, extensive spatial datasets, and a high-resolution atmospheric transport model. Based on the results of this analysis the authors conclude that the US Environmental Protection Agency (EPA) underestimates methane emissions nationally by 50%. The study found that methane emissions due to the animal husbandry and fossil fuel industries have larger greenhouse gas impacts than indicated by existing inventories.
A source of methane in the atmosphere are leaks from natural gas distribution systems. A partnership between the Environmental Defense Fund (EDF) and Google Earth has released the first interactive maps showing methane leaks from gas distribution systems under the streets of Boston, Indianapolis and part of New York City.
The Administration's strategy is to target reducing methane emissions from several sources;
- Landfills: The Environmental Protection Agency (EPA) will propose updated standards to reduce methane from new landfills and determine whether to update standards for existing landfills.
- Coal Mines: The Bureau of Land Management (BLM) will release an Advanced Notice of Proposed Rulemaking (ANPRM) to gather public input on the development of a program for addressing waste mine methane on lands leased by the Federal government.
- Agriculture: The US Department of Agriculture (USDA), EPA and the Department of Energy (DOE) will jointly release a “Biogas Roadmap” outlining voluntary strategies to accelerate adoption of methane digesters to reduce U.S. dairy sector greenhouse gas emissions by 25 percent by 2020.
- Oil and Gas: The EPA will assess several potentially significant sources of methane and other emissions from the oil and gas sector. If EPA decides to develop additional regulations, it will complete those regulations by the end of 2016. In addition the BLM will propose updated standards to reduce venting and flaring from oil and gas production on public lands.
Improved data collection: The Administration intends to implement better data collection and measurement will to improve the understanding of methane sources and trends and enable more effective reduction of methane emissions.
As part of that strategy in April, 2014, EPA released five technical white papers that present information on potentially significant sources of emissions in the oil and gas sector and options for reducing emissions. According to the Energy Information Administration (EIA), in 2011 there were an estimated 504,000 producing gas wells and an estimated 536,000 producing oil wells in the U.S. Natural gas development is expected to increase by 44% from 2011 through 2040 and crude oil and natural gas liquids (NGL) are projected to increase by approximately 25% through 2019.
Two of the white papers prepared by the U.S. EPA Office of Air Quality Planning and Standards (OAQPS) describe methane emissions due to (1) gas emissions when fracked and refracked oil wells are brought into production and (2) leaks in gas production (natural gas wells including shale gas) , processing and transmission.
Emissions from completions and ongoing production of hydraulically fractured oil wells
One of the activities identified as a potential source of emissions to the atmosphere during oil development is hydraulically fractured oil well completions which are operations conducted to bring a new fracked oil well into production or to maintain or increase the well’s production capability as a result of refracking. The EPA white paper estimates of nationally uncontrolled methane emissions from hydraulically fractured oil well completions range from 44,306 tons (40,194 tonnes) per year to 247,000 tons (224,000 tonnes) per year. There is no data on the proportion of this methane that is vented, flared or captured and sold.
Leaks are defined as methane emissions that occur at onshore production, processing and transmission facilities. It does not include leaks in gas distribution systems (see EDF and Google Earth above). This includes leak emissions from natural gas well pads, oil wells that co-produce natural gas, gathering and boosting stations, gas processing plants, and transmission and storage infrastructure. The white paper cites estimates of approximately 332,662 tonnes of potential methane leak emissions from gas production, 33,681 tonnes from gas processing, and 114,348 tonnes from gas transmission.
The EPA has just (Jan 29, 2015) issued a call inviting small businesses, governments, and not-for-profit organizations to participate in a Small Business Advocacy Review (SBAR) Panel that will focus on the development of a rule to reduce emissions of greenhouse gases including methane and volatile organic compounds (VOCs) for the oil and natural gas industry. The agency intends to add equipment and processes, including hydraulically fractured oil wells and leaks from new and modified well sites, to those currently covered by existing standards.
EPA plans to propose a rule this summer (2015) and take final action in 2016.
Largest reservoirs of methane
An indirect effect of global warming is the destabilization of methane hydrates by warming ocean currents on the floor of the ocean. Methane hydrates are the largest reservoir of organic carbon on Earth and there is the potential that the total volume of methane hydrates being destabilized by warming ocean currents could be significant. Methane is also stored in shallow Arctic reservoirs of peat, such as submarine and terrestrial permafrost, which is also being affected by global warming.