A close look at fugitive methane emissions from natural gas
Natural gas is booming in the United States. Production has increased by 20 percent in the last five years, fueled largely by technological advances in shale gas extraction. Other countries–including China–are now studying our experience with this abundant new resource.
But the growing role of natural gas in the U.S. energy mix hasn’t come without controversy. Natural gas development poses a variety of environmental risks. In addition to habitat disruption and impacts on local water and air quality, one of the most significant concerns is the climate impact resulting from the “fugitive methane emissions” that escape into the atmosphere from various points along the natural gas supply chain.
So what are fugitive methane emissions, and how big of a problem are they? How do emissions from natural gas compare to those from coal? And are there ways to mitigate them? The answers to these questions will help us better understand how natural gas development will affect climate change.
What Are Fugitive Methane Emissions, and How Do They Contribute to Climate Change?
Methane, the primary component of natural gas, is a powerful greenhouse gas–25 times stronger than carbon dioxide (CO2) over a 100-year time horizon and 72 times stronger over a 20-year horizon. Though methane represents only about 10-12 percent of all U.S. greenhouse gas emissions, it is a significant driver of short-term warming, and reducing methane emissions can help slow the rise in global temperatures.
While proponents of natural gas often tout its “green” credentials—combustion of natural gas emits roughly one-half the CO2 of coal combustion—this is not the whole story. When it is extracted from the well, natural gas is composed of roughly 83 percent methane, after processing and through the point of delivery, it is more than 90 percent methane. Producing, processing, and transporting of natural gas can release some of this methane into the atmosphere. Accidental methane leaks and routine venting–which together, make up fugitive methane emissions–reduce the comparative climate advantage of natural gas for electricity generation. Plus, at current estimated leakage rates, fugitive emissions actually make compressed natural gas a questionable choice for fuel-switching in cars and trucks.
What Is the Extent of the Problem?
There is still considerable uncertainty over the amount of fugitive methane emitted over the lifetime of a natural gas well. However, some aspects generate little debate—namely, that emissions from natural gas production are substantial and occur at every stage of the natural gas life cycle, from pre-production through production, processing, transmission, and distribution. The U.S. Environmental Protection Agency (EPA) estimates that more than 6 million metric tons of fugitive methane leaked from natural gas systems in 2011. Measured as CO2-equivalent over a 100 year time horizon, that’s more greenhouse gases than were emitted by all U.S. iron and steel, cement, and aluminum manufacturing facilities combined.
Many ongoing studies aim to provide more clarity on the extent of fugitive methane emissions from natural gas. We’ll get a clearer picture when data from these studies is looked at in conjunction with industry data reported to the EPA Greenhouse Gas Reporting Program. But with about 500,000 existing natural gas wells, thousands of miles of pipeline, and a growing interest in natural gas development, we’ll never have a truly complete picture of the amount of methane being emitted.
Is Natural Gas Better than Coal?
Considerable media attention has focused on the question of whether gas is “better” than coal from a climate perspective. On the one hand, this question sets a low bar for environmental performance—studies have found that by just about any measure, every other energy source is less damaging to the environment and public health than coal. On the other hand, this is an important benchmark, since more than 30 percent of U.S. natural gas is used for electric power generation and more than 90 percent of all U.S. coal consumption is used for this purpose. The question has also received heightened attention as many older, inefficient coal-fired power plants retire and natural gas-fired plants provide a growing share of total electric power generation.
At the point of combustion, natural gas is roughly half as carbon-intensive as coal. However, this comparison fails to account for upstream fugitive methane emissions. When used for electric power generation, natural gas is typically much more efficient than coal, but natural gas is not a more energy efficient fuel option for all uses—for example, in the case of vehicles. Also, if fugitive methane emissions exceed 3 percent of total gas production, natural gas’s climate advantage over coal disappears over a 20-year time horizon.
The critical question is: Given the current extent of U.S. natural gas production—and the fact that production is projected to expand by more than 50 percent in the coming decades—are we doing everything we can to ensure that emissions are as low as is technologically and economically feasible? The answer to that question today is clearly “no.”
How Can We Mitigate Natural Gas’s Impact?
Numerous cost-effective technologies can reduce fugitive methane emissions, which will curb global warming and save money for energy companies and for consumers. While some companies are voluntarily implementing these technologies to varying degrees, the industry is vast, including thousands of participants with diverse market interests. Much more can be done. In a working paper to be published later this week, we discuss in greater detail the scale of the methane leakage issue, as well as numerous policy and technology pathways for state and federal authorities to begin limiting these harmful emissions.
Ultimately, cleaning up fugitive methane should be an urgent priority to help slow the rate of climate change in the near-term. We’ll also need policies to significantly reduce carbon dioxide emissions—from the combustion of natural gas as well as other fossil fuels. To stabilize the climate at safe levels by mid-century, we need to address GHG emissions from all sources. Fugitive methane is one important, cost-effective opportunity that we can begin addressing today.