Natural gas emits significantly less carbon dioxide than either coal or gasoline when burned, but its ability to help reduce overall greenhouse gas emissions has been questioned. In the latest contribution to the debate, a study published this week by Duke University researchers concludes that switching to abundant shale gas as an energy source is unlikely to be much help in addressing climate change, unless it’s only one part of a comprehensive strategy to reduce emissions.
The study, published online in the journal Environmental Science and Technology, concluded that natural gas use has “modestly reduced” U.S. greenhouse gas emissions, mostly because so far it has displaced higher-emissions energy sources such as coal and petroleum, rather than lower-emissions sources such as nuclear and hydroelectric plants and renewable resources such as solar and wind.
But even though natural gas produces lower carbon dioxide emissions, some of the benefit is lost because natural gas production and distribution releases methane, a highly potent greenhouse gas, into the atmosphere. (A study published in February in Science reported that methane emissions may be 50 percent higher than U.S. government estimates, though the scientists concluded that leakage was not great enough to negate the climate benefits of switching from coal to natural gas as a fuel for electricity.)
In a future scenario in which natural gas continues mostly to replace coal and oil, the global reduction in greenhouse gas emissions would be so small that by itself, it wouldn’t do that much to slow climate change, the Duke researchers calculated.
In electrical generation, for example, greenhouse gas emissions would be cut by 5.1 percent between 2010 and 2040, while emissions from heating residential and commercial buildings would fall by 3.3 percent during that period. In the transportation sector, replacing gasoline with compressed natural gas (CNG) or liquefied natural gas (LNG) vehicles could cut greenhouse gas emissions by as much as 25 percent for buses and 30 percent for cars and light trucks. (From the U.S. Environmental Protection Agency, here’s a chart showing how much various sectors of the economic contribute to total greenhouse gas emissions.)
But if abundant natural gas is so cheap in the future that it makes cleaner energy sources such as nuclear, hydroelectric and renewables uncompetitive, the climate benefit would be lost. “If natural gas is substituting for zero-emissions fuels, it will increase emissions,” explained the study’s primary author, Duke University Energy Initiative director Richard Newell.
The study concluded that for natural gas use to have a significant impact upon climate, it would have to be part of a larger, comprehensive public and private sector energy strategy focused on reducing greenhouse gas emissions. The private sector strategy would include a mix of energy sources and stronger incentives to employ new, cleaner energy sources, and the use of carbon capture and sequestration to reduce emissions from remaining coal-burning power plants.
Predicting the impact of natural gas use on climate change is further complicated by the global nature of the economy, Newell said. If the availability of cheap, abundant natural gas in North America leads companies to put industrial plants here instead of in countries that remain reliant upon coal, it might result in a net global savings in greenhouse gas emissions, he said.
Newell said that while natural gas isn’t a panacea for climate change, it isn’t necessarily a villain, either. “One has to take a comprehensive view on the energy system, in order to identify opportunities for reducing total emissions,” he said. “If one takes a narrow focus on one technology or sector, reductions in one place may simply show up somewhere else.”
Critics of fracking may view the study as further evidence that natural gas has been oversold as a remedy for climate change. “It’s been widely promoted that way by the industry, and politicians have picked up on that,” said Cornell University professor of ecology and environmental biology Robert Howarth, the author of a much-debated paper on greenhouse gas emissions from the fracking process. “Personally, I think natural gas is as bad or worse than any other fossil fuel, when it comes to climate change. We really need to go the renewable route.”