The United States is poised to bet its energy future on natural gas as a clean, plentiful fuel that can supplant coal and oil. But new research by the Environmental Protection Agency—and a growing understanding of the pollution associated with the full "life cycle" of gas production—is casting doubt on the assumption that gas offers a quick and easy solution to climate change.
Advocates for natural gas routinely assert that it produces 50 percent less greenhouse gases than coal and is a significant step toward a greener energy future. But those assumptions are based on emissions from the tailpipe or smokestack and don't account for the methane and other pollution emitted when gas is extracted and piped to power plants and other customers.
The EPA's new analysis doubles its previous estimates for the amount of methane gas that leaks from loose pipe fittings and is vented from gas wells, drastically changing the picture of the nation's emissions that the agency painted as recently as April. Calculations for some gas-field emissions jumped by several hundred percent. Methane levels from the hydraulic fracturing of shale gas were 9,000 times higher than previously reported.
When all these emissions are counted, gas may be as little as 25 percent cleaner than coal, or perhaps even less.
Even accounting for the new analysis, natural gas—which also emits less toxic and particulate pollution—offers a significant environmental advantage. But the narrower the margins get, the weaker the political arguments become and the more power utilities flinch at investing billions to switch to a fuel that may someday lose the government's long-term support.
Understanding exactly how much greenhouse gas pollution comes from drilling is especially important, because the Obama administration has signaled that gas production may be an island of common political ground in its never-ending march toward an energy bill. The administration and Congress are seeking not just a steady, independent supply of energy, but a fast and drastic reduction in the greenhouse gases associated with climate change.
Billions of cubic feet of climate-changing greenhouse gases—roughly the equivalent of the annual emissions from 35 million automobiles—seep from loose pipe valves or are vented intentionally from gas production facilities into the atmosphere each year, according to the EPA. Gas drilling emissions alone account for at least one-fifth of human-caused methane in the world's atmosphere, the World Bank estimates, and as more natural gas is drilled, the EPA expects these emissions to increase dramatically.
When scientists evaluate the greenhouse gas emissions of energy sources over their full lifecycle and incorporate the methane emitted during production, the advantage of natural gas holds true only when it is burned in more modern and efficient plants.
But roughly half of the 1,600 gas-fired power plants in the United States operate at the lowest end of the efficiency spectrum. And even before the EPA sharply revised its data, these plants were only 32 percent cleaner than coal, according to a lifecycle analysis by Paulina Jaramillo, an energy expert and associate professor of engineering and public policy at Carnegie Mellon University.
Now that the EPA has doubled its emissions estimates, the advantages are slimmer still. Based on the new numbers, the median gas-powered plant in the United States is just 40 percent cleaner than coal, according to calculations ProPublica made based on Jaramillo's formulas. Those 800 inefficient plants offer only a 25 percent improvement.
Other scientists say the pollution gap between gas and coal could shrink even more. That's in part because the primary pollutant from natural gas, methane, is far more potent than other greenhouse gases, and scientists are still trying to understand its effect on the climate—and because it continues to be difficult to measure exactly how much methane is being emitted.