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Natural gas as a transition fuel: A bridge too far?

20 July 2016
Amber Lin

Amber Lin

Amber Lin is a sophomore at Princeton University, pursuing a degree in civil and environmental engineering and architecture. She plans a career in the sustainable design of urban...


The use of natural gas to mitigate climate change is a serious point of contention in American politics today. President Barack Obama publicized the idea of natural gas as a “bridge fuel” in 2014, saying that it “can power our economy with less of the carbon pollution that causes climate change.” While Democratic nominee Hillary Clinton once agreed, in the new Democratic platform—heavily influenced by Bernie Sanders—the “bridge fuel” concept is gone, replaced by a plan that incentivizes wind and solar over natural gas. The GOP, on the other hand, continues to support expanded use of all fossil fuels: coal, oil, and natural gas. Natural gas consumption is increasing more than any other energy source in the United States, so understanding its trajectory is especially important.

What exactly does a “bridging” process entail? The label of “bridge fuel” or “transition fuel” suggests that natural gas is capable of both cutting coal-based greenhouse gas emissions and giving way to an emissions-free future. To serve as a bridge, natural gas must completely replace coal—something that is already happening. But how long natural gas will be needed, and how it will be phased out in the transition to a renewables-only future, is still up in the air.

When viewed through a long-term economic lens, natural gas is not going to facilitate the transition to an emissions-free future, for two reasons: the economic disadvantages of renewables-compatible gas power plants compared with other gas plants, and the economic challenges that come with locking in an energy infrastructure. There are possibilities for natural gas infrastructure to continue operating in a carbon-neutral world, but they rely on the advent of viable biofuel and carbon capture and storage technology.

Cheap, plentiful, and clean? Natural gas is seen as a promising alternative to coal because it is not only cheap and much cleaner-burning, but can also generate electricity on demand—unlike intermittent energy sources such as the sun and wind. Recent technological developments in hydraulic fracking—a process in which a mixture of water and chemicals is injected under high pressure into rock formations to release the gas inside—have contributed to low natural gas prices. Opposition to fracking focuses on its environmental effects on groundwater and on greenhouse gas emissions from methane, the main component of natural gas. These arguments, however, do not consider the long-term implications of expanded natural gas infrastructure.

In a 2013 paper, Michael Levi, now a Special Assistant to the President for Energy and Economic Policy, provided a rough deadline for contextualizing natural gas emissions within climate change goals: To limit global warming to a maximum of 2 degrees Celsius over pre-industrial levels, Levi wrote, global gas consumption would have to peak around 2020 to 2030.

Between a rock and a hard place. When constructing a new natural gas power plant, there are two options: a combined cycle or an open cycle. A combined-cycle power plant produces electricity with relatively high efficiency and low carbon emissions: When the gas burns, it heats and compresses air to spin a turbine and power a generator. A heat recovery system captures waste heat, which is routed to a nearby steam turbine to generate even more power. Combined-cycle plants have low operating costs, but because high capital costs must be offset, these plants are built to produce baseload power—available 24 hours a day. Open-cycle gas turbine plants lack the steam cycle, so their thermal efficiency is much lower, and their carbon emissions per unit of electricity generated are slightly higher. Their running costs are much higher than a combined-cycle plant, but they have a much lower start-up cost, so they are often built as “peakers,” plants that run only to support other power infrastructure during hours of high demand or when solar or wind isn’t available.

Considering the two choices in the larger context of natural gas as a “transition fuel,” a dilemma appears: To build the bridge, combined-cycle is what is needed—a consistent, efficient, power source that can effectively replace coal. But for a combined-cycle natural gas plant to be economically feasible, it would typically need 15 to 20 years to make up for start-up costs, and even longer to become profitable. This means that a combined-cycle plant built in 2016 would break even no sooner than 2031, and would have to run for several more decades to be a worthwhile investment. Levi’s 2030 limit for peak emissions translates to major fossil fuel reductions after 2030. Owners and backers, however, will not want to shut down gas plants that are just beginning to generate a profit. Thus, building combined-cycle plants in 2016 without an explicit understanding of their necessarily temporary nature—and with no financial incentives for early closures in the future—defeats the purpose of natural gas as a “transition fuel.”

Why not focus on open-cycle plants instead? While “peakers” make sense as backups for future renewable energy sources, they don’t make sense right now. In the current infrastructure, because the electricity they produce is relatively expensive, peakers' use is kept to a minimum—only those hours when electricity demand is particularly high ("peak demand”). The higher electricity production cost means that peakers cannot be profitably used to displace coal. Closed-cycle plants can help build the bridge but cannot close it, and open-cycle plants can help close the bridge but cannot build it. Neither type of plant is both economically feasible in the long run, and powerful enough to meet today’s demand while cutting emissions in time to mitigate climate change. However, when natural gas is branded as a “transition fuel” in politics and in popular media, this crucial detail is rarely mentioned.

A costly lock-in. In 2010, natural gas generated about 988 million megawatt-hours of electricity at utility-scale facilities. By 2015, generation had risen to 1,335 million megawatt-hours, an increase of 35 percent, and natural-gas-fired electricity generation is expected to reach a record level this year. Aided by government subsidies and “green” image boosts, energy companies are building more and more gas plants every year.

As natural gas takes over the energy market, investors increasingly base their decisions on the bandwagon effect—with less consideration for sustainability and long-term economic performance. While cheap natural gas is now causing nuclear plants such as Diablo Canyon to shut down prematurely, steadily improving solar and wind technology could do the same to natural gas plants 15 to 20 years from now—ruining the economics of the closed-cycle plants that are currently being built. If the United States is serious about its emissions-reduction pledges, investors might want to take their money elsewhere; investing in solar and wind now could accelerate progress toward climate goals and ultimately be more profitable than investing in natural gas.

Problems for the people. The growth of any industry affects the jobs outlook. In the natural gas industry, roles such as architects, surveyors, and construction managers offer flexibility, but those such as pipelayers, derrick operators, and wellhead pumpers do not. This specialization is not a problem for the first phase of the natural gas transition; workers with experience in oil and coal will have transferrable skills in the natural gas industry, and workers new to the workforce will jump right in. But for the eventual transition from natural gas to solar and wind power, there is not as much overlap.

From both an economic and moral perspective, it is not beneficial to train a workforce to specialize in an industry that could be phased out within 10 to 20 years. And even if the timeline associated with the two-degree-Celsius goal is not strictly enforced by governing bodies, a transition to renewables, whether in 10 or 50 years, is inevitable if human society wishes to avoid runaway climate change. The American Petroleum Institute estimates that in 2015, the natural gas industry supported 9.8 million jobs in the United States and 8 percent of GDP. As this number continues to grow, it will expand the workforce trained for the natural gas industry and unable to make the leap to renewables, leading to future unemployment and negative impacts on the national and global economies.

If the industry continues to grow at its current rate, institutions such as unions and industry associations will emerge to provide representation for workers. There is currently only one trade association, the American Petroleum Institute, that represents all aspects of America’s oil and natural gas industry, but a growing industry could lead to the formation of additional associations. While beneficial to workers in the near term, these groups could present a problem when it comes time for the inevitable phase-out of natural gas. On the other hand, these organizations could aid in a smoother economic transition—for example, by lobbying for government help to retrain workers. This is not a new concept—“Just Transition” is a framework that has been developed by trade unions working to minimize hardships for workers and their communities in the transition to a low-carbon and climate-resilient economy; the next step would be to turn this framework into laws and government programs. But even if steps are taken to help workers, the money will have to come from somewhere; the shutdown of the Diablo Canyon nuclear plant will cost the Pacific Gas and Electric Company $350 million in compensation and retraining for employees—a deal that persuaded the local union to agree to the shutdown.

And it isn’t just power plant jobs that will be affected. Natural gas currently heats one out of four homes in the United States; natural gas vehicles are replacing some gasoline vehicles; and products such as plastics, polymers, tires, and detergent all consume natural gas in their production. The growth of these industries requires more and more pipeline to transport natural gas—not just from gas fields to power plants, but also to individual homes, public buildings, gas stations, and factories.

Building bridges to last. While natural gas might not be able to mitigate climate change strictly by acting as a “bridge fuel,” there are possibilities for natural gas to assist in creating a carbon-neutral world in other ways. For example, natural gas infrastructure could remain in place for many decades if its carbon emissions could be eliminated through carbon capture and storage. Or natural-gas-burning power plants could switch to carbon-neutral biogas—made from plants, rather than shale gas—as a fuel source. These possibilities, though, require advanced technology that is not yet economically feasible.

If the United States is to head down the path of dramatically increasing natural gas consumption, it must also develop technology that can allow natural gas infrastructure to become carbon-emissions-free and to work in harmony with renewables. For natural gas to be built up and then taken down within the next few decades—as a true “bridge fuel” should be—the United States would need to abandon closed-cycle plants that have not yet made a profit, supply the workforce with new jobs, and fight opposition from not only natural gas companies but also related industries. While natural gas may be the most convenient method of quickly reducing carbon emissions, it cannot currently be considered a “transition fuel” to a carbon-free future. The misleading label distracts policymakers from developing technologically and economically sound solutions, and should be abandoned if progress is to be made.

Editor’s note: This article contains corrections made after publication. An error about the number of US natural-gas-fired electricity generation plants was corrected to show the recent rise (in megawatt-hours) in electricity generation from natural gas, and an incorrect description of a finding in Michael Levi’s 2013 paper was removed. Changes were also made to clarify the economics of "peaker" plants and why their use is kept to a minimum, and to clarify that natural gas consumption is increasing more than other US energy sources in absolute terms.