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Natural Gas Takes Another Climate Change Hit


by Bill Chameides | September 14th, 2011
posted by Erica Rowell (Editor)

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Is natural gas too clean?

Natural Gas As a Transition Fuel: A Bridge Too Far?

For about a decade now, natural gas has been hailed by many as the fossil-fuel bridge to a future low-carbon economy (see here and here), and I was one of them (though not without concerns).

The reasoning seemed simple enough. The bulk of electrical power generated worldwide comes from burning coal, the most carbon-intensive fossil fuel. Its composition has the highest carbon-to-hydrogen ratio, so for each unit of energy generated, burning it produces more carbon dioxide (CO2). The rise in coal-burning-generated electricity is a scary prospect for the climate. This fact has prompted activists globally to lobby, argue, and in some cases protest against the construction of new coal-fired power plants.

By contrast, natural gas is the fossil fuel with the lowest carbon-to-hydrogen ratio and so emits the least amount of CO2 per unit of electricity generated or (mile driven). And so it’s been reasoned that, given the challenges of meeting our energy needs from renewable sources, why not use natural gas as a transition fuel — to wean us off coal as more viable renewable energy technologies are developed and implemented?

A good idea but not without caveats. For years it was believed there wasn’t enough natural gas to compete economically with coal. That applecart was upset with the implementation of horizontal drilling/hydrofracturing technology, by which tight rock formations like shale, formerly thought impenetrable, are fractured by the pumping of huge amounts of water, chemicals and sand at high pressure to get at the natural gas for extraction. Suddenly the amount of potentially recoverable natural gas resources from shale deposits skyrocketed here, and around the world. The shale gas rush was on, presumably for the betterment of the environment.

Unfortunately the glow is off the natural gas rose.

Natural Gas Benefits Potentially Fractured and Leaking

Concerns about the environmental impacts of hydrofracking have been growing, especially around the possible degradation of groundwater and drinking water. While U.S. fracking operations continue largely unabated, should these environmental impacts turn into intractable problems, natural gas as a transition fuel will become a bridge to nowhere.

The major component of natural gas is methane, a greenhouse gas some 20 times more effective as a global warmer than CO2 (over a 100-year time horizon). This means that vented or leaked natural gas during well development, extraction and/or distribution could be large enough to offset or even overwhelm the climate benefits of burning natural gas over coal.

Dirty Is Better?

Now Tom Wigley of the National Center for Atmospheric Research reports on a study that shows a switch to natural gas won’t be a climate winner because it’s too “clean.”

Let me back up a second. Coal, in addition to being the most carbon-intensive fossil fuel, is also the dirtiest. Alongside its carbon and hydrogen content, coal is loaded with nasties: toxins like mercury, radioactive elements, and sulfur which, when burned, leads to sulfur dioxide (SO2) emissions — and it’s the SO2, Wigley argues, that’s the rub.

Once in the atmosphere, SO2 is converted into tiny sulfate particles. For the most part these particles are bad news — when inhaled they can cause serious acute and chronic health problems, and contribute to acid rain.

SO2 is a problem America’s been working to mitigate for some time [pdf], ever since the fledgling Environmental Protection Agency set the first ambient air quality standard for it in 1971. In the years since, emissions standards for SO2 have been ratcheted ever tighter. In 1990, the Clean Air Act Amendments’ acid rain program mandated emission reductions from coal-fired power plants; the reductions were achieved through the use of low-sulfur coal and emissions controls using a cap-and-trade framework. Most recently the Obama administration finalized rules designed to meet objections made by the Supreme Court over the proposed tightening of emissions by the George W. Bush administration.

One Man’s Pollution Is Another’s Growth

Meanwhile, other countries, especially in Asia, have not been as concerned about sulfur pollution, and their growing use of coal is growing SO2 emissions. This is a bad thing, right? Not quite, Wigley argues.

You see, those sulfate particles also affect the climate: By reflecting sunlight back out to space, they cool the planet. In effect, the emissions of sulfur from coal act to offset the global warming that comes from emissions of CO2. Because sulfate particles are removed from the atmosphere in a week or so and CO2 stays in the atmosphere for centuries, slowing the use of coal can have the perverse effect of exacerbating rather than ameliorating global warming. This is a conundrum that Wigley first pointed out in a seminal paper published in the journal Nature in 1991.

Wigley uses this same basic concept to argue that switching from coal to natural gas will not really help from a climate point of view. His result assumes that the developing world adopts sulfur pollution controls and is even worse if significant natural gas leakage occurs.

Interesting result, but we shouldn’t get carried away. The media have been spinning Wigley’s results as a vote for coal-fired power plants. Indeed, Wigley states in his summary that “the substitution of gas for coal as an energy source results in increased rather than decreased global warming for many decades.” A bit of an overstatement in my opinion.

  1. The differences in the coal and natural gas scenarios are very small — given the uncertainties in the parameters used in the calculations, I think it’s probably better to say there’s no discernible climate benefit from natural gas.
  2. The results depend upon the effectiveness of the pollution controls used in coal-fired power plants and natural gas production and distribution. Should the controls be more effective than Wigley assumes (and technology often advances faster than is projected), then the climate benefits of natural gas will grow.

Probably most important, it does not necessarily follow from this work that we should stick with coal. Using air pollution to counter global warming pollution is a Faustian bargain that we should consider very carefully before signing on the dotted line. Wigley acknowledges this in concluding th
at “decisions regarding further exploitation of gas reserves should be based on resource availability (both gas and water), the economics of extraction, and environmental impacts unrelated to climate change.”

How will all this shake out? Not sure yet. But there’s an interesting subplot to this drama. Many in the natural gas industry have expressed concern about global warming while touting their product as a solution. Will they change their tune if it turns out that natural gas is not climate-friendly?

filed under: Asia, carbon dioxide, carbon dioxide emissions, climate change, coal, energy, faculty, fossil fuels, global warming, health, methane, natural gas, pollution, toxins, water
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