Natural gas may be a cleaner-burning energy source than coal, but making the switch isn’t likely to slow global warming any time soon, according to a new study in the journal Climatic Change.
Reducing coal use may cut down on carbon dioxide, but its affect on the earth’s warming trend isn’t quite so simple, according to Tom Wigley, a senior research associate at the National Center for Atmospheric Research. Among other considerations, methane leaks from gas production and in transmission lines could negate the climate benefit until well into the 22nd Century:
When gas replaces coal there is additional warming out to 2,050 with an assumed leakage rate of 0%, and out to 2,140 if the leakage rate is as high as 10%. The overall effects on global-mean temperature over the 21st century, however, are small.
Just how much methane currently leaks during transmission — or would leak during a massive push to burn more gas — is still an open question. So is methane’s affect on climate change compared to carbon dioxide — a Cornell University study released earlier this year suggested methane was far worse for the climate than old estimates from the U.S. Environmental Protestion Agency had suggested. The American Petroleum Institute, among other industry groups, was highly critical of that method.
In the new study, Wigley uses a more conservative model for methane’s impact on climate change than the Cornell researchers. But the switch from coal to gas — dropping our coal use by 50 percent by 2050, he suggests — would come with a couple of planet-warming chemical side-effects.
For one, somewhat paradoxically, the sulfur dioxide released from burning coal has a cooling effect that’d be lost in a switch to natural gas.
Just how much methane escapes into the atmosphere before being burned is another, less certain, variable, Wigley writes. “Unless leakage rates for new methane can be kept below 2%, substituting gas for coal is not an effective means for reducing the magnitude of future climate change,” he writes in his conclusion. (You can read the study here.)
A study commissioned by the City of Fort Worth suggested improvements in pipe connections to limit methane leakage have been targeted as the prime targets for improving the natural gas industry’s affect on air quality.
As the Los Angeles Times reports today, Wigler considered a range of methane leak rates. Even in a perfect scenario, he found, the switch from coal wouldn’t do much to slow climate change for decades:
Even assuming there is no leakage — unlikely, most would agree — the switch analyzed by Wigley would still add to Earth’s overall average temperature through about 2050. After that, temperatures would fall, but only by a few tenths of a degree Fahrenheit. If a substantial amount of methane leaks, the warming trend will last until 2140, he found.
Bear in mind, the most widely reviewed studies predict a global average temperature rise of 5.4 degrees Fahrenheit by 2100 under current fossil-fuel consumption rates.
“Relying more on natural gas would reduce emissions of carbon dioxide, but it would do little to help solve the climate problem,” said 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.”