Tuesday, September 13, 2011

Switching from coal to natural gas would do little for global climate, study indicates

September 08, 2011
BOULDER—Although the burning of natural gas emits far less carbon dioxide than coal, a new study concludes that a greater reliance on natural gas would fail to significantly slow down climate change.
Coal, natural gas, and climate: Shifting from coal to natural gas would have limited impacts on climate, new research indicates. If methane leaks from natural gas operations could be kept to 2.5% or less, the increase in global temperatures would be reduced by about 0.1 degree Celsius by 2100. The reduction in global temperatures would be more minor with higher methane leakage rates. (Courtesy Springer, modified by UCAR.)

The study by Tom Wigley, who is a senior research associate at the National Center for Atmospheric Research (NCAR), underscores the complex and sometimes conflicting ways in which fossil fuel burning affects Earth’s climate. While coal use causes warming through emission of heat-trapping carbon dioxide, it also releases comparatively large amounts of sulfates and other particles that, although detrimental to the environment, cool the planet by blocking incoming sunlight.

The situation is further complicated by uncertainty over the amount of methane that leaks from natural gas operations. Methane is an especially potent greenhouse gas.

Wigley’s computer simulations indicate that a worldwide, partial shift from coal to natural gas would slightly accelerate climate change through at least 2050, even if no methane leaked from natural gas operations, and through as late as 2140 if there were substantial leaks. After that, the greater reliance on natural gas would begin to slow down the increase in global average temperature, but only by a few tenths of a degree.

“Relying more on natural gas would reduce emissions of carbon dioxide, but it would do little to help solve the climate problem,” says Wigley, who is also an adjunct professor at the University of Adelaide in Australia. “It would be many decades before it would slow down global warming at all, and even then it would just be making a difference around the edges.”

The study will appear next month in the peer-reviewed journal Climatic Change Letters.

A small impact on temperatures

The burning of coal releases more carbon dioxide than other fossil fuels, as well as comparatively high levels of other pollutants, including sulfur dioxide, nitrogen oxides, and particles such as ash. Since natural gas emits lower levels of these pollutants, some energy experts have proposed greater reliance on that fuel source as a way to slow down global warming and reduce the impacts of energy use on the environment.
But the effects of natural gas on climate change have been difficult to calculate. Recent studies have come to conflicting conclusions about whether a shift to natural gas would significantly slow the rate of climate change, in part because of uncertainty about the extent of methane leaks.

Wigley’s new study attempts to take a more comprehensive look at the issue by incorporating the cooling effects of sulfur particles associated with coal burning and by analyzing the complex climatic influences of methane, which affects other atmospheric gases such as ozone and water vapor.

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