Natural gas as fuel harms climate more than diesel: Study

A new report in the journal Science concludes that switching buses and trucks from traditional diesel fuel to natural gas could actually harm the planet's climate.

Although burning natural gas as a transportation fuel produced 30 per cent less planet-warming carbon dioxide emissions than burning diesel, the drilling and production of natural gas could cause leaks of methane, a greenhouse gas 30 times more potent than carbon dioxide. Those methane leaks negated the climate change benefits from the use of natural gas as a transportation fuel, the study points out.

The study was conducted by scientists at Stanford University, the Massachusetts Institute of Technology and the Department of Energy's National Renewable Energy Laboratory.

 The study concluded that there was already about 50 per cent more methane in the atmosphere than the earlier estimates by the Environmental Protection Agency, a signal that more methane was leaking from the natural gas production chain than previously thought.

According to Adam R Brandt, an assistant professor in the department of energy resources at Stanford, switching from diesel to natural gas, was not a good policy from a climate perspective.

The study, however, does conclude that switching from coal-fired power plants - the nation's largest source of carbon pollution - to natural gas-fired power plants would still lower planet-warming emissions over all.

Natural gas emitted only half the carbon pollution of coal, and even considering the increased pollution from methane leaks, natural gas-fired plants led to less emissions than coal over 100 years, according to the study.

According to the report, bottom-up leakage estimates like EPA's were consistently smaller than those derived from atmospheric sampling of methane on a regional scale. The study panel, found the national atmospheric estimates to be the most reliable. Bottom-up estimates could mislead, according to the authors, because their sampling was too spotty to catch the few ''superemitters''-the broken valve or poorly maintained compressor-that appeared to account for much of total methane emission. The panel concluded that actual methane emissions were 1.25 to 1.75 times the EPA estimate.

Atmospheric chemist Paul Wennberg of the California Institute of Technology in Pasadena, who was not involved in the Science study said, the one-in-thousand superemitter ''does seem to be a problem.'' He added, ''it's economically and environmentally straightforward to address that.''

The study found that fracking for shale gas-a target of environmentalists of late, seemed to be a minor source, with the largest source probably natural gas production and processing. In contrast, gas distribution-including leaks like those recently reported around Washington DC-was a lesser source.