Written by Dr. Arvind Ravikumar
There is much to cheer about the recent climate agreement signed last December at the 21st Conference of Parties (COP 21) in Paris, France to reduce greenhouse gas emissions and limit global temperature rise to below 2° C. Whether countries will implement effective policies to achieve this agreement is a different question. Leading up to the Conference in Paris, countries proposed their intended nationally determined contributions (INDCs). These refer to the various targets and proposed policies pledged by all countries that signed the United Nations Framework Convention on Climate Change on their intended contribution to reduce global warming. The United States, among other things, is banking on the recently finalized Clean Power Plan by the Environmental Protection Agency (EPA) – this policy aims to reduce US greenhouse gas (GHG) emissions from the power sector by 26 to 28% in 2030, partly by replacing high-emitting coal fired power plants with low-emitting natural gas fired plants, and increased renewable generation (primarily wind and solar). Electricity production by natural gas fired plants is therefore expected to increase over the next few decades, acting as a ‘bridge-fuel’ to a carbon-free economy. Even though the US Supreme Court recently halted the implementation of the Clean Power Plan, the EPA anticipates that it will eventually be upheld.
A major component of natural gas is methane. This is a highly potent greenhouse gas whose global warming potential (i.e. ability to increase the Earth’s surface temperature through the greenhouse effect) is 36 times that of carbon dioxide in long-term (100-year impact) and over 80 in the near-term (20-year impact). Although carbon dioxide is a major component of US greenhouse gas emissions (see Fig. 1), it is estimated that methane contributes around 10% of the total emissions. Thus, given its significantly higher global warming potential, methane emissions and leakage can potentially erode the climate benefits of declining coal production.
Methane emissions are fairly diversified across natural and man-made sources. Figure 2 shows the sources of methane emissions in the US (2013) as estimated by the EPA through its GHG monitoring program. While 50% of emissions can be attributed to agriculture and waste-disposal activities, we can see that about 30% of methane emissions come from the oil and gas industry. Much of this can be attributed to the recent boom in non-conventional or shale gas production through fracking technology. The combination of low natural gas prices and higher demand from the power sector makes it imperative to reduce methane emissions as much as technologically feasible.
Currently, methane leaks occur at all stages of the natural gas infrastructure – from production and processing, transmission to distribution lines in major cities. While the global warming effects of higher methane concentrations are fairly well understood, there is currently little consensus on the magnitude of emissions from the natural gas infrastructure. For example, a recent study found that the average methane loss in all distribution pipelines around Boston was about 2.7%, significantly higher than the 1.1% reported in inventory estimates to the EPA. Another study that was published in the academic journal, Science, showed that various independent measurements of methane leakage rate across the US infrastructure varied from about 1% to over 6%. Climate benefits of switching from coal to natural gas fired power plants would critically depend on this leakage rate.
[…], detailed measurements from the Barnett shale region in Texas showed that just 2% of the facilities in the region account for 50% of all the methane emissions.
To better estimate methane leakage, the Environmental Defense Fund (EDF), a non-profit organization based in Washington, DC, organized and recently concluded a series of 16 studies to find and measure leaks in the US natural gas supply chain. While some of the results are currently being analyzed, much of the data show that conventional inventory estimates maintained by the EPA have consistently underestimated the leakage from various sources. It was shown that the Barnett shale region in Texas that produces about 7% of the nation’s natural gas, emitted 90% more methane compared to EPA estimates. To complicate matters further, until recently, estimates from atmospheric top-down data measured using satellites and aircrafts significantly exceeded land-based bottom-up measurements using methane sensors. On a similar note, detailed measurements from the Barnett shale region in Texas showed that just 2% of the facilities in the region account for 50% of all the methane emissions. Such a small fraction of large emission sources will further complicate direct measurements where typically only a small fraction of the facilities in a region are measured. While the EDF and other studies have been instrumental in our current understanding of methane leaks in the US and its contribution to greenhouse gas emissions, much work is required to understand sources, and most importantly, ways to cost-effectively monitor, detect and repair such leaks.
Aerial footage of the recent natural gas leak from a storage well in Aliso Canyon near LA. The leak is estimated to have released 96000 metric tons of methane, equivalent to about 900 million gallons of gasoline burnt and $15 million worth of natural gas. Source: Environmental Defense Fund, 2015.
Methane leakage in the context of global warming has only recently caught public attention – see here, here and here. In addition to greater awareness in business and policy circles, significant efforts are required to identify economically viable leak detection and repair programs. Currently, the industry standard to detect methane leaks include high-sensitivity but high-cost sensors, or low-cost but low-sensitivity infrared cameras. There is an immediate need to develop techniques that can be used to cost-effectively detect leaks over large areas (e.g. thousands of squared miles). From a regulatory perspective, EPA has released proposed regulations to limit methane leaks from the oil and gas industry. This comes on the heels of the goals set by the Obama administration’s Climate Action Plan to reduce methane emissions from the oil and gas sector by 40 to 45% from 2012 levels by 2025. These regulations require oil and gas companies involved in the entire natural gas life cycle to periodically undertake leak detection and repair procedures, depending on the overall leakage levels. The final rule is expected to be out sometime in 2016.
The success of the Clean Power Plan in reducing greenhouse gas emissions will significantly depend on the strength of the proposed regulations to curb methane leaks. We now have a better estimate of fugitive emissions (leaks) of methane from the US natural gas infrastructure. Concurrently, there should be a greater focus on developing cost-effective programs to detect and repair such leaks. It was recently reported that replacing old pipelines with newer ones in the gas distribution network in a city is effective in reducing leaks, and improving public safety. With a considerably higher global warming potential than carbon dioxide, methane has the potential to erode the climate benefits earned by switching from high emitting coal plants to low emitting natural gas power plants. Ensuring that does happen will take a coordinated effort and commitment from both the industry and government agencies.
Arvind graduated with a PhD in Electrical Engineering from Princeton University in 2015 and is currently a postdoctoral researcher in Energy Resources Engineering at Stanford University. Somewhere later in grad school, he became interested in the topics of energy, climate change and policy. Arvind is an Associate Editor at Highwire Earth. You can read more about his work at his personal website.