The Gas Is Always Greener When It Leaks Less
The great promise of natural gas, we’re often told, is that it will be better for the climate than other fossil fuels. In fact, this can come true only if very little of the fuel is allowed to escape, unburned, into the air.
The trouble is, we don’t know how much natural gas leaks -- as it is extracted, processed, transported and used -- and some evidence suggests the amount may be more than we have assumed. As the U.S. gears up to use more of the fuel, not only for electricity and home heating but also to power cars and trucks and for export, the need to find out how much is getting away is urgent.
This is exactly what experts convened by the Department of Energy recommended last August. So far, their call has gone unanswered.
The reason natural gas has a reputation for being gentle on the climate is that burning it emits almost a third less carbon dioxide than burning oil does, and almost 45 percent less than burning coal does.
But when methane, the principal component of natural gas, floats directly into the air, it has a much stronger greenhouse effect than carbon dioxide has -- 25 times stronger over the course of a century and, over 20 years, 72 times stronger. (The time span makes a difference because methane breaks down in the atmosphere faster than carbon dioxide does.)
The maximum leakage we can afford is 3.2 percent of the total amount of natural gas used, scientists from the Environmental Defense Fund and three universities recently figured out. Any more than that, and using natural gas leads to more heat being trapped in the atmosphere for some time than using coal does.
The best guess so far on how much is leaking is just 2.4 percent. However, this number, from the U.S. Environmental Protection Agency, is based not on direct measurements but on limited data collected 20 years ago.
Recent measurements taken near a natural-gas field north of Denver indicate that the actual amount of methane escaping there is higher -- about 4 percent.
This study determined leakage by sampling the air in the vicinity of natural-gas facilities, which is a more accurate way of assessing leakage. Yet it would be better to monitor methane directly at the points where it is escaping.
Environmental Defense Fund scientists are taking such measurements now at select drilling sites in four big natural- gas-producing regions in the U.S. Eventually, they plan to take similar readings on leaks from transmission pipes and storage facilities.
Careful measurements are also needed where compressed or liquefied natural gas is being provided for cars and trucks. A certain amount of methane leaks during fueling and use of these vehicles. Because methane is especially potent in the short term, converting a fleet of cars from gasoline to compressed natural gas will, for many years, make climate change worse, according to the same scientists who calculated the 3.2 percent limit for total methane leakage.
In order for such a fleet conversion to produce net climate benefits immediately, well-to-wheels leakage must be reduced to at least 1.6 percent, from the current estimated 3 percent. For heavy trucks, the leak rate would need to come down to 1 percent.
A new escape route for methane will be opened as the U.S. begins exporting some of its natural-gas bounty. (With natural- gas prices at $9 per million BTU and higher in Europe and $17 in Asia, a new facility in Louisiana to liquefy gas for export is on the drawing board.) Methane can escape during liquefaction, shipping and regasification at the receiving end. All these leaks, too, have to be measured.
What’s ultimately needed is a full accounting of all methane escaping from the natural-gas supply chain. Such an effort is expected to cost many millions of dollars and require cooperation by federal agencies involved in energy, the environment, transportation and trade. In calling for the effort last August, the Energy secretary’s Shale Gas Production Subcommittee wisely recommended that the White House Office of Science and Technology Policy coordinate the job and make sure it gets funded and started immediately.
In the meantime, as the subcommittee also said, natural-gas producers should begin their own voluntary efforts to directly measure leaks, even as they work to reduce them.
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