Natural-gas operations could leak enough methane to tarnish their clean image.
How clean is natural gas? Although it is often lumped in with coal and oil, many in the energy industry are at pains to point out that burning gas to generate electricity produces fewer greenhouse-gas emissions than does burning other fossil fuels. Certainly, countries claim reductions in carbon emissions when they switch from coal to gas, as Britain did on a large scale in the 1990s. The growing popularity of shale formations as a source of gas has re-energized the debate over its environmental impact. To release the gas, engineers must split the rock by injecting fluid under high pressure, a process called fracking. Last year, researchers from Cornell University in Ithaca, New York, said that with this taken into account, carbon emissions associated with shale gas were no better — or were worse — than those from coal.
Industry maintains that the problem has been exaggerated, and many scientists agree. Sorting fact from fiction has been difficult, however, because nobody had any independent data — until now.
As discussed on page 139, a study led by scientists from the US National Oceanic and Atmospheric Administration (NOAA), headquartered in Washington DC, and the University of Colorado in Boulder looked at methane and other emissions from a natural-gas field north of Denver, where fracking methods are used to open up sand formations.
They estimated cumulative emissions from the field using not industry reports or conceptual models, but concentrations of pollutants in air samples. This is important because the atmosphere does not misrepresent data or make mistakes; nor does it bend to ideology or political will.
Emissions from natural-gas operations could be substantially higher than was thought.
The data suggest that methane emissions from natural-gas operations could be substantially higher — and so be worse for global warming — than was thought. At works in the Denver-Julesburg Basin, methane emissions were roughly double the official estimate.
This will by no means settle the debate. The NOAA scientists had to make assumptions to convert atmospheric data to cumulative emissions from a vast energy complex. They readily acknowledge substantial uncertainty in their calculations, and estimate that between 2% and 8% of the methane produced from wells in the Denver-Julesburg Basin is lost to the atmosphere, with a best guess of 4%.
These numbers, which are higher than estimates from Cornell and the US Environmental Protection Agency (EPA), should serve as a red flag to the gas industry, policy-makers and the academic community. Researchers will need to confirm the findings, reduce the uncertainties and determine emissions from other locations. But the issue clearly warrants attention. The study should also be a reminder that although it is necessary for the industry to collect data on its practices and run calculations, independent monitoring and verification are needed.
More generally, the study further complicates understanding of what is considered the world's cleanest fossil fuel. Many in industry and science have talked about using gas as a bridge fuel for the transition from coal to cleaner sources of electricity, but the picture is unclear.
In many places, including the United States, gas-fired electricity is likely to be significantly cleaner than coal in terms of carbon emissions even with the extra methane leakage — if only because newer gas-fired plants are much more efficient than the behemoths that provide most coal-fired electric generation. By contrast, a modelling study by Tom Wigley, a climate scientist at the US National Center for Atmospheric Research in Boulder, last year found that switching from coal to natural gas would actually increase global temperatures for decades, by reducing emissions of pollutants that reflect solar radiation back into space (T. M. L. Wigley Climatic Change 108, 601–608; 2011). In the end, natural gas might be preferable to coal just because it reduces harmful air pollution. But the climatic benefits are murky at best.
The good news is that the natural-gas industry has the capacity to reduce methane leakage by cleaning up its operations. Technologies are already available to capture methane during fracking rather than venting it into the atmosphere when bringing a gas well online. As it happens, the EPA is currently considering mandatory regulations that encourage such activities by limiting various pollutants from natural-gas operations. These regulations would indirectly reduce methane emissions, and the EPA must press forward.
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Gas and air. Nature 482, 131–132 (2012). https://doi.org/10.1038/482131b
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