Shale gas extracted through fracking is unlikely to alter climate change projections by reducing greenhouse gas emissions, scientists have said.
Researchers from Duke University's Energy Initiative said the use of natural gas instead of higher-emission energy sources will not significantly alter total emission without policies set out to reduce greenhouse gasses.
Published in a special issue of Environmental Science and Technology, the team looked at the net effect of greenhouse gas emissions from various energy sources.
The main benefit of shale gas, the authors said, was that it could lower the cost of energy production, meaning there was more money to achieve climate goals.
Researcher Richard Newell said: "Over the range of scenarios that we examine, abundant natural gas by itself is neither a climate hero nor a climate villain."
They said shale gas was cleaner than fuels like coal and oil, but extracting it and transporting it can result in methane emissions – the precise levels of which were unknown.
"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 researcher Daniel Raimi.
"The net effect on US greenhouse gas emissions appears likely to be small in the absence of policies specifically directed at greenhouse gas mitigation."
The study found that the climate benefits of natural gas are reduced if there are a lot of methane emissions, and that recent evidence suggests methane emissions from shale could be higher than the US Environmental Protection Agency is currently estimating.
Raimi continued: "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."
Newell added: "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.
"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 maximising the potential benefits of natural gas."