It’s been nearly a month since Robert Howarth’s paper claiming that shale gas was worse for climate change than coal made its big splash in the New York Times. I expressed quite a bit of skepticism at the time – and readers of this blog proceeded to dissect the paper in the comments. Now, the Department of Energy’s National Energy Technology Laboratory (NETL) has applied ISO standard methodology, and a substantial understanding of industry operations, to do the calculation itself (PDF of a presentation last week at Cornell). Its conclusion? Used to generate electricity, natural gas – conventional or not – results in far less emissions than coal.
Using a 100-year global warming potential and assuming an average power plant, unconventional gas results in 54% less lifecycle greenhouse gas emissions than coal does. Even using a 20-year global warming potential, as Howarth controversially argues one should, the savings from substituting unconventional gas for coal are almost 50%. The NETL study acknowledges – and explores – a range of uncertainties. But it finds nothing close to the problems that Howarth claims.
The NETL documents don’t address the Howarth study explicitly, but if you flip to page 25, you’ll see a big part of the discrepancy explained. Some readers will recall that Howarth found a large fraction of produced gas from unconventional wells never made it to end users, assumed that all of that gas was vented as methane, and thus concluded that the global warming impacts were huge. As the NETL work explains, though, 62% of that gas isn’t lost at all – it’s “used to power equipment”.
The NETL work also does a much more careful job looking at things like losses from long distance transmission. In addition, it doesn’t include losses from local distribution, since there’s no local distribution involved in using gas for power generation.
Bottom line: Those who were skeptical of the Howarth study were reacting correctly. There’s still much useful work to be done, but for now, the NETL work is a far more useful guide for thinking through the gas emissions issue.