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Making Sense of Gas vs. Coal and Climate: A Look at the Recent Paper by Tom Wigley

September 14, 2011

The last few months have seen a flurry of academic papers investigating whether using natural gas for power generation creates more global warming than using coal for power generation.  A few have reached the startling conclusion that using gas for power is just as bad, or worse, than coal. The most recent of these is by Tom Wigley, a global leader in climate science, and therefore bears special examination.  As we’ll argue below, natural gas is no climate panacea, especially over the time scales that Wigley examines.  We need zero-carbon energy. But it is also important to consider how we get to that future, and natural gas – coupled with carbon capture and storage and tight controls on methane leaks – will likely have a big role to play there in the next few decades.  It is critical that we accurately account for the climate impacts of gas, and we don’t agree with Wigley’s approach in two key areas.

Wigley does not dispute that switching electrical generation from coal to gas will reduce CO2 emissions.  But according to Wigley much – or all – of the climate benefit from the reduced carbon would be offset by two other changes in emissions: 1) methane leaks and releases from increased gas development and 2) reductions of sulfates from coal burning.

While nearly all of the press coverage of the paper has focused on the methane, the sulfate is more important than the methane in Wigley’s models for any reasonable natural gas leak rate.  The sulfate is more important even if the leak rate for gas is twice what we think it is.  Let’s take a look at the sulfate issue first.

It’s well understood that coal-fired power plants emit sulfur compounds, which react in the atmosphere to form a haze of sulfate particles that reflect incoming sunlight and cool the planet.  These sulfates are a very serious air pollutant, increasing respiratory illnesses and deaths. They are also the major cause of acid rain. These public health and environmental impacts have driven successful regulations to reduce sulfur.  Largely through use of scrubbers, the US has halved sulfur from power plants over the past 20 years.

The drop has been much faster in Europe (pdf, p. 16).  During the same period, coal consumption has dropped a bit in Europe, and in the US it has increased.

Sulfur emissions do remain high in other parts of the world, including China, where roughly one new coal plant has come on line every week over the past few years. While there is no chance that these new coal plants will retire any time soon, sulfur emissions from coal plants in China have declined significantly since about 2006, due to installation of scrubbers – even while coal plants have continued to come on-line at a very rapid pace.

Thus we see no support for Wigley’s assumption that over the next 50 years conversion from coal to gas will cause sulfur reductions.  Coal to gas conversions that do occur will most likely happen after the sulfur has already been removed, and we will already be experiencing the climate response.  That train has left the station, and we are benefiting from the cleaner air.

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