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Natural Gas: Not Clean Enough

This post is a synopsis of Energy Innovation’s issue brief describing the research and findings from its latest study, “Natural Gas versus Coal: Is Natural Gas Batter for the Climate?,” which has been published in Electricity Journal. 

New research, led by Energy Innovation’s Director of Research Chris Busch, compares the climate impacts associated with electricity generated from natural gas versus coal. The findings conclude that, even under the best of circumstances, electricity generated by natural gas-fired power plants can only make a modest dent in abating climate change—and, if developed poorly, with serious methane leaks, or if used to displace energy efficiency or renewable energy, natural gas could instead seriously contribute to the problem.

Natural gas is made up of mostly methane, which can be emitted through intentional venting or accidental leakage at all stages of the natural gas system, from extraction to processing, transmission, distribution, and end-use. Methane is a powerful greenhouse gas (GHG); it causes 28 times more global warming than carbon dioxide on a mass basis over a 100-year period. On a 20-year basis, the impact of methane is 84 times larger than carbon dioxide, and its impact is 120 times larger when first released.

Energy Innovation’s analytical framework estimates the GHG emissions caused by generating one megawatt-hour (MWh) of electricity from both coal and natural gas power plants, taking into account their three largest sources of emissions: methane, smokestack carbon dioxide (emitted from fuel combustion at the power plant), and upstream carbon dioxide (emitted during production and transmission of fuel prior to reaching the power plant). A power plant’s efficiency significantly drives its GHG intensity, which can vary widely across new, existing, and retired (coal) power plants. Recent research (Brandt et al. 2014) has increased certainty about the rate of methane emissions from the natural gas system, indicating it is roughly in the range of two to four percent for the United States on average.

“New” represents the efficiency for typical power plants constructed today. “Average” is the average plant efficiency of all plants operating in 2012. “Retired coal” is the average efficiency for coal plants that have recently shut down. The methane leakage rate is shown in parenthesis for each gas scenario.

These results illustrate natural gas’ advantage over coal in smokestack emissions, yet methane emissions diminish this gain. When comparing first-year impacts, both new and average gas plants with high methane leakage rates would be more GHG intensive than new or average coal plants. After 20 years, one MWh from new gas is 16–40 percent less GHG intensive than average coal, depending the level of methane emissions. After 100 years, the advantage of natural gas increases; it offers an improvement of 44–52 percent above coal. Yet, by this time, emissions reductions must be much more ambitious than this if we are to power civilization in a way that enables a safe and stable climate. So while it may be beneficial to use existing natural gas capacity to help shut down existing coal plants, investment in many more natural gas plants in the future may not be advisable, especially if they replace (rather than enable) increased electricity generation from renewables.

This article was originally posted on Energy Innovation’s blog page.