CHARLESTON, W.Va. -- Switching power plants from coal to natural gas will not help to significantly slow down global warming, according to the latest in a series of studies to examine the much promoted role for gas as a "bridge fuel" to cleaner energy production.

The study, published late last week in the peer-reviewed journal Climate Change Letters, found that substitution of gas for coal would result in increased -- rather than decreased -- global warming for many decades.

Study author Tim Wigley, senior research associate at the National Center for Atmospheric Research, in Boulder, Colo., used computer simulations to project temperature changes in various scenarios where coal is replaced by gas for energy production.

The study is important for West Virginia, where political leaders are pushing the boom in Marcellus Shale gas drilling as a huge economic development winner. Along with touting job creation, natural gas companies promote the notion that they provide a cleaner option over coal.

But Wigley found that a 50 percent reduction in coal use, along with a corresponding increase in natural gas use, would lead to a slight increase in worldwide warming for the next 40 years of about 0.1 degree Fahrenheit. The reliance on natural gas could then gradually reduce the rate of global warming, but temperatures would drop by only a small amount, compared to the 5.4 degrees of warming projected by 2011 under current energy trends, he found.

"Relying more on natural gas would reduce emissions of carbon dioxide, but it would do little to solve the climate problem," Wigley said. "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."

Coal is considered the nation's largest source of global-warming pollution, representing a third of U.S. greenhouse emissions, equal to the combined output of all cars, trucks, buses, trains and boats. Most scientists recommend the nation swiftly cut carbon dioxide emissions, reducing them by about 80 percent below 2000 levels by mid-century to avoid the worst consequences of climate change.

The study, published late last week in the peer-reviewed journal Climate Change Letters, found that substitution of gas for coal would result in increased -- rather than decreased -- global warming for many decades.

Study author Tim Wigley, senior research associate at the National Center for Atmospheric Research, in Boulder, Colo., used computer simulations to project temperature changes in various scenarios where coal is replaced by gas for energy production.

The study is important for West Virginia, where political leaders are pushing the boom in Marcellus Shale gas drilling as a huge economic development winner. Along with touting job creation, natural gas companies promote the notion that they provide a cleaner option over coal.

But Wigley found that a 50 percent reduction in coal use, along with a corresponding increase in natural gas use, would lead to a slight increase in worldwide warming for the next 40 years of about 0.1 degree Fahrenheit. The reliance on natural gas could then gradually reduce the rate of global warming, but temperatures would drop by only a small amount, compared to the 5.4 degrees of warming projected by 2011 under current energy trends, he found.

"Relying more on natural gas would reduce emissions of carbon dioxide, but it would do little to solve the climate problem," Wigley said. "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."

Coal is considered the nation's largest source of global-warming pollution, representing a third of U.S. greenhouse emissions, equal to the combined output of all cars, trucks, buses, trains and boats. Most scientists recommend the nation swiftly cut carbon dioxide emissions, reducing them by about 80 percent below 2000 levels by mid-century to avoid the worst consequences of climate change.

But some scientists are becoming increasingly concerned about methane emissions that leak from gas-drilling operations, in part because methane is a more potent greenhouse gas than carbon dioxide.

Robert Howarth, a Cornell University ecologist who authored a widely cited paper on the subject earlier this year, cautions that switching from coal to natural gas shouldn't divert the country from bringing on more renewable energy sources.

"It's not saying we should keep burning coal," Howarth said in an interview. "It's that we should do more to move to what we need to do in the longer term anyway."

Gas industry supporters, though, point to another study by researchers at Carnegie Mellon University in Pittsburgh, reporting the previous conventional wisdom that natural gas produces half the greenhouse emissions of coal.

"We favor extraction of Marcellus Shale natural gas as long as the extraction is managed to minimize adverse economic, environmental and social impacts," said Chris Hendrickson, one of the Carnegie Mellon study's authors.

The Carnegie Mellon study used different assumptions, including older estimates of methane leakage from drilling, that could account for its different results.

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.