Context is everything

I’m grateful to James Barth for pointing out an unintentional ambiguity in my last column. I failed to make it clear that, like the job creation data I mentioned, the statistic I quoted on GHG reduction—“27% since 2005”—relates only to the electricity generation sector, which accounts for roughly a third of CO2 emissions in the U.S. I did not mean to imply a 27% reduction in overall emissions. The figure came from a November 2016 article in Politico that used data from the Sierra Club to describe U.S. success in meeting the interim goals of President Obama’s Clean Power Plan, which focuses on reducing CO2 from power plants. For comparison, the Energy Information Agency (EIA) states that “carbon dioxide (CO2) emissions from electricity generation totaled 1,925 million metric tons (MMT) in 2015, the lowest since 1993 and 21% below their 2005 level.” EIA’s preliminary 2016 data for the electric generation sector projects a further reduction in CO2 from 2015 levels to 1,821 MMT in 2016, roughly 26% below 2005 levels according to my amateur calculations.

Various commenters have attributed this progress to the retirement of coal burning power plants, energy efficiency improvements and increased electricity generation from renewable energy and natural gas. But there’s a big fly in the ointment for environmental claims about the use of natural gas to generate electricity. The spoiler, of course, is methane, which the EPA acknowledges is 84-87 times more climate-damaging than CO2 in the climate-critical 20-year near-term.

The Environmental Defense Fund (EDF) began researching this issue in 2011, partnering with more than 100 academic institutions and the petroleum industry. Two studies undertaken by EDF in 2013-2014 in partnership with the University of Texas concluded that methane emissions in the oil and gas sector were reassuringly low, a view hotly challenged by other environmental organizations. This past March, a new peer-reviewed study by Purdue University and EDF, which analyzed air samples collected by Purdue’s Airborne Laboratory for Atmospheric Research, found that natural gas power plants actually emit anywhere from 21 to 120 times more methane than previously thought, casting serious doubt on electricity-sector GHG estimates and regulations based on them.

Published in Environmental Science & Technology, the study appears to refute EDF’s own prior studies as well as the industry’s self-reporting to the EPA, which has focused on combustion emissions and downplayed methane leakage throughout the supply chain from gas field to compressors, pipelines, delivery and end use. While the new study concluded that natural gas is “still cleaner relative to burning coal,” that’s pretty faint praise compared to emissions-free solar and wind power that make up an increasing share of electricity generation. In this new informational context, there’s welcome news that the EPA’s inspector general will investigate how the EPA estimates methane emissions for the national GHG inventory, and the U.S. Court of Appeals for DC has ruled that the EPA cannot stall implementation of new rules designed to reduce methane emissions in oil and gas operations.


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