fossil fuels

Does replacing coal with natural gas reduce emissions enough to be a valid interim power source until we develop greener power?

David Lyon, a scientist with the Environmental Defense Fund, said “it’s a great question, but it’s always going to be specific to situations.” And, he said, you need to know a lot of details to get an answer.

Lyon and his colleagues have spent years researching the different pieces of this question. While there are many factors to consider, including the efficiency of the power plants in question, one of the most important is how much methane is leaking from wells, valves, pipelines and other equipment that carries the gas to power plants. Natural gas is composed primarily of methane, which is itself a greenhouse gas that traps much more heat per pound than carbon dioxide. So while a natural gas-burning power plant emits less carbon dioxide—or CO2—than a coal plant, those savings can be offset by any methane that leaks on its way to the plant.

“If it’s greater than a 2.7 percent loss rate,” Lyon said, “then there will be a period of time during which the climate impacts due to the methane emissions cause more damage than the benefits of having less CO2 from combustion. So I guess the question is what’s the leak rate of gas that we’re using in the United States?” he said. “What we found is that at least nationwide it’s pretty close.”

Nationally, the rate may be slightly below that 2.7 percent threshold, Lyon said, but there’s a lot of variation depending on where the gas is coming from. In the Permian Basin, which stretches across parts of Texas and New Mexico and is the nation’s most productive oil and gas region, Lyon and colleagues found that about 3.7 percent of all the methane produced leaks into the atmosphere. That means a new gas plant using Permian Basin gas would likely have a worse impact on the climate than any coal plant it replaced, at least in the short term. In parts of Pennsylvania’s Marcellus Basin, however, the leak rate is below 1 percent.

Lyon’s answer points to another complicating factor: while methane is a more potent greenhouse gas than CO2, it breaks down much more quickly. So switching from coal to gas could be worse for the climate when examined over a 20-year time frame, for example, but better over the course of a century. Some science and policy experts say that the urgency of limiting warming over the next few decades means continuing to invest in new natural gas power plants carries great risks.

Perhaps most important, however, is the fact that renewable sources such as wind and solar are available, and are in many places competitive with or even cheaper than new natural gas plants. Lyon said it is often politics, rather than technical feasibility, that stands in the way of switching directly to renewables. And while gas can be better than coal under the right circumstances, he said, “it’s never going to be as good as renewables.” 

Nicholas Kusnetz

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