May 15, 2014
Abundant Shale Gas Will Not Likely Alter Climate Predictions
April Flowers for redOrbit.com - Your Universe Online
Climatologists and energy scientists know that replacing higher-emission energy sources with natural gas will reduce greenhouse gas emissions.
According to a new study from Duke University, however, even without policies specifically designed to reduce greenhouse gases, abundant shale gas will not cause a substantial change in total emissions. The study was published in a recent issue of Environmental Science and Technology.
The general assumption is if natural gas is abundant and less expensive, consumers will choose to use more natural gas rather than fuels such as coal, renewables and nuclear power. The only way this will have a positive effect on the climate, however, is if the greenhouse gas emissions of carbon dioxide and methane caused by natural gas use is lower than the emissions that would have come from the other energy sources.
Previous studies have shown that using natural gas instead of coal for electricity production, gasoline in transportation, and electricity in building would decrease greenhouse gas emissions. On the other hand, the production and consumption of natural gas causes higher emission levels than renewables and nuclear power.
"Over the range of scenarios that we examine, abundant natural gas by itself is neither a climate hero nor a climate villain," said Richard Newell, Gendell Professor of Energy and Environmental Economics and director of the Duke University Energy Initiative.
Proponents of natural gas favor gas from shale formations for a cleaner, inexpensive replacement for fuels such as coal and oil—which emit more local air pollutants and carbon dioxide. The problem is that processing and transporting the gas can result in emissions of methane. Although significant research is underway to understand this, scientists are uncertain about the precise level of these methane emissions.
Methane, according to the US Environmental Protection Agency (EPA), is the second most prevalent greenhouse gas created by human activity. It is also emitted from natural sources such as wetlands and livestock. Though it has a shorter lifetime in the atmosphere, methane is much more efficient at trapping radiation than carbon dioxide, making its impact on the environment 20 times greater.
"We find that so far increased natural gas has mostly taken the place of coal, but looking forward there also may be increased consumption for sectors such as industry, as well as some degree of displacement of zero-emission sources such as renewables and nuclear," said Daniel Raimi, associate in research at the Energy Initiative. "The net effect on U.S. greenhouse gas emissions appears likely to be small in the absence of policies specifically directed at greenhouse gas mitigation."
The team used a variety of evidence, including models of two hypothetical futures, to reach their conclusions. The first "future" involved natural gas production and prices following a "reference case" scenario. The second "future" saw increased shale gas production which lowered prices and encouraged higher consumption. In the analysis, the team also accounted for a range of methane emissions scenarios, ranging from 25 percent below to 50 percent above the levels estimated by the EPA.
"The fact that increased shale gas doesn't have a huge climate impact on its own doesn't mean it's not important. If broad climate policy is enacted, having abundant natural gas could be very helpful by making it cheaper for society to achieve climate goals," Newell said. "If natural gas is expensive, then it will be more costly to switch away from fuels that have higher greenhouse gas emissions, such as coal and oil. But keeping methane emissions low is essential to maximizing the potential benefits of natural gas."
If there are a lot of methane emissions, the positive benefits of using natural gas are mitigated; however, "recent evidence suggests methane emissions may be higher than the EPA currently estimates, it's not clear how this new information will affect those estimates," Raimi said. "Reducing methane emissions is important, but even if methane emissions from natural gas systems are significantly higher than current EPA estimates, we did not find this significantly alters the impact of abundant natural gas on long-term national or global greenhouse gas emissions pathways."