The increasing prominence of natural gas as a foundation fuel for the U.S. economy has heightened attention on methane emissions from natural gas production, processing, and delivery. Natural gas is composed primarily of methane, a potent greenhouse gas (GHG), and the direct release of methane can offset the climate benefits of increase use of natural gas for combustion. Therefore, understanding the level of methane released is critical to assessing the climate impacts of natural gas use.
This is where data recently released from the U.S. Environmental Protection Agency (EPA) adds to our understanding. New revised EPA estimates published in April show a natural gas system with low methane emissions on a long-term declining trend, providing further support that natural gas can be relied on to reduce greenhouse gas emissions. I recently completed a short analysis of the EPA GHG Inventory and what it implies for methane emissions and natural gas systems and I’ve summarized some of the its findings here.
EPA’s annual U.S. Inventory of Greenhouse Gases and Sinks from 1990 through 2011 across the U.S. economy covers all major and minor greenhouse gases including carbon dioxide, methane, nitrogen oxides, and other gases. EPA accounts for the greater global warming potential of methane and reports all data using a carbon-dioxide equivalent metric, thereby putting carbon dioxide and methane emissions data on equal footing. Each year natural gas systems account for a very small portion of greenhouse gas emissions; in 2011, methane from gas systems contributed only 2.2 percent of economy-wide GHGs.
What’s new in the inventory this year? First, EPA made substantial revisions to its estimates of natural gas systems. EPA cut its estimates for methane released by natural gas systems by a third after receiving new data and recalculating emissions from field production. Specifically, activities related liquids unloading were recalculated with new emissions data and activity factors and accounted for a large portion of the reductions. Alongside completions and work overs with hydraulic fracturing, which was revised slightly upwards, emissions from field production in total were cut by 55 percent, accounting for the majority of the changes.
Second, we see a confirmation of a long-term downward trend in methane emissions. Methane released from natural gas systems declined 10 percent between 1990 and 2011, even as production and consumption hit all-time record highs in 2011. Shrinking emissions amid rising gas production means improvements have outpaced growth.
Natural gas utility activities have improved at an even faster rate. Distribution system emissions dropped 16 percent since 1990, even as the industry added 300,000 miles of distribution mains to serve 17 million more customers, a 30 percent increase in both activities. The reason for the declines is improved industry practices, participation in EPA’s voluntary emissions reduction program Natural Gas STAR, and utility investments into new infrastructure, in particular the increased installation of plastic pipe as replacement of older cast-iron and steel pipelines.
What do these improvements in emissions mean in the context of rapidly growing natural gas production? The new EPA Inventory implies an effective emissions rate of production of 1.5 percent. This is taken by dividing the amount of methane released by total natural gas production that year. This low emissions rate is contrast to prior EPA inventories that pegged the rate at 2.2 to 2.4 percent, depending on the year examined. New science will continue to refine this number, but this year’s inventory signifies directionally where new information points us and how new and better data informs public understanding of the GHG profile of natural gas production and use.
Finally, the improvements in the gas system are leading the way in economy-wide methane reductions. Each year, natural gas systems account for about one quarter of all methane released, which includes direct emissions stemming from activities like agriculture, landfills, petroleum production, and others. Despite this quarter share, since 2007 (the all-time high for both methane and total greenhouse gas emissions) improvements to natural gas system methane emissions accounted for 76 percent of all methane reductions economy-wide. In other words, the gas system has outpaced all other economic sectors in reducing its methane footprint.
Understanding methane emissions is essential to inform the public debate about the benefits of natural gas to our climate. We expect the 2014 Inventory to include additional data and ongoing data collection from government, academia, and industry will help refine understanding of this important issue. As our knowledge of the system improves, actual emissions are expected to continue shrinking. The signs are positive and point to a continuously improving natural gas system.
For more information, please see my analysis “Finding the Facts: What the EPA Greenhouse Gas Inventory Says About Methane Emissions from Natural Gas Systems”