Natural gas not so benign?

In the US, a bill that seeks to replace diesel with natural gas in heavy vehicles is being discussed in the Congress. Besides cutting oil imports, and at the same time reduce greenhouse gas emissions, it is argued 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.
Robert Howarth, professor of ecology and environmental biology at Cornell University thinks the move will aggravate global warming.

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.

His numbers are significantly different than those researchers at MIT came up with a year ago. (On a CO2 equivalent grams per megajoule basis, they scored diesel at 10.7 and gasoline at 14.4, with natural gas splitting the difference at 12.5). The two studies make different assumptions about the strength of methane as a greenhouse gas, and the amount of methane leakage, for example.

The MIT study concludes that there is a benefit from switching to natural gas, all told, but it might not be worth the cost or the hassle. Making more efficient gasoline and diesel vehicles might work better, and be a faster way to reduce greenhouse emissions, it suggests.

The moral of the story: the times we live in call for detailed studies before making any leap into a new energy source or technology. Better to be sure rather than repent?