And speaking of using natural gas for transportation (as in part of my earlier post, The true face of shale gas), there’s the whole nasty issue of leaks.

Natural Gas May Be Worse for the Planet than Coal:

This week the U.S. Congress heard testimony supporting a bill that would push to replace diesel with natural gas in heavy vehicles. It’s an attempt to cut oil imports, and at the same time reduce greenhouse gas emissions. Part of the argument is that natural gas is substantially cleaner than diesel, and results in the emission of about 25 percent less greenhouse gas.

But experts are warning that natural gas might not be as clean as it seems.

In fact, using natural gas rather than diesel in vehicles could actually increase climate change, says Robert Howarth, professor of ecology and environmental biology at Cornell University. “You’re aggravating global warming more if you switch,” he says.

Howarth is basing his conclusion on a preliminary analysis that includes not only the amount of carbon dioxide that comes out of a tailpipe when you burn diesel and natural gas, but also the impact of natural gas leaks. Methane, the main component of natural gas, is much more effective at trapping heat than carbon dioxide, so even small amounts of it contribute significantly to global warming. When you factor this in, natural gas could be significantly worse than diesel, he says. Using natural gas would emit the equivalent of 33 grams of carbon dioxide per megajoule. Using petroleum fuels would emit the equivalent of just 20 grams of carbon dioxide per megajoule.

Howarth goes further, suggesting that natural gas could even rival greenhouse gas emissions from mining and burning coal–the dirtiest of fossil fuels. He says it’s “not significantly better than coal in terms of the consequences of global warming” and is calling for a moratorium on extracting natural gas from shale, which requires more energy (and so emits more greenhouse gases) than extracting it from conventional natural gas sources.

Oops.

To hang some numbers on the magnitude of current methane leaks, see the US Dept. of Energy’s report, Emissions of Greenhouse Gases in the United States 2007 [PDF] which shows (page 5) that the top three sources of methane emissions in the US are:

  • Natural gas systems, 176.6 million metric tons of CO2 equivalent
  • Landfills, 169.0
  • Enteric fermentation (i.e. livestock farts and burps), 138.5

So, in addition to those existing leaks, add in tens of millions of new vehicles and connectors (since many people will likely use in-home refueling gizmos), and you suddenly have the potential for vastly larger impact. While Howarth’s analysis is still “preliminary”, I suspect now that he’s opened the door, a lot of people will be rushing through, calculators in one hand and a list of assumptions in the other.

Stay tuned.


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