Because burning natural gas produces about half as much carbon dioxide (CO2) per unit of energy as coal, many consider it an important transition fuel to carbon-neutral, climate-friendly sources of energy. However, the colorless, odorless gas has a downside: It contains more than 80% methane (CH4), a potent greenhouse gas that absorbs and retains 86 times more energy than CO2 over a 20-year period.
If too much methane leaks out as natural gas is drilled and pumped from the ground, it could negate any climate benefits derived from switching fuels.
Now, a new survey of methane leaks in a major natural gas- and coal-producing region in the United States suggests that without more stringent regulations to capture CH4 emissions, natural gas extraction could be worse for the climate than coal within 20 years.
Natural gas production in the United States has skyrocketed over the past decade, thanks largely to improvements to hydraulic fracturing and horizontal drilling—extraction techniques in which water, sand, and chemicals are pumped into the ground to break apart gas-holding rock formations. Previous studies have found that this nationwide production system isn’t leaking enough methane to make coal a better choice, but discrepancies between the methods used in different studies and the wide range of results have made the findings controversial.
In their new analysis, Ren et al. used a Cessna 402B research aircraft to quantify methane emissions from a 4,235-square-kilometer region of the Marcellus Formation in Pennsylvania and West Virginia, which accounts for about 40% of total U.S. shale gas production. Over the course of six flights in the summers of 2015 and 2016, they took air samples upwind and downwind of the natural gas operations, pulling air through a tube installed at the nose of the plane and analyzing its chemical composition. Then, they compared the levels of methane to background measurements collected in the region, taking into account other known sources of methane pollution such as cattle farms, coal mines, and landfills.
Previous studies have established a threshold at which natural gas becomes worse for global warming than coal: a leak rate of 2.4% of total natural gas production per year over 20 years. The leak rate from natural gas extraction operations in the sampled area of the Marcellus Formation was around 3.9% of the total production, exceeding that threshold, the team found. To ensure that natural gas extraction and combustion are a net benefit to the climate compared with coal, more stringent regulations for capturing those fugitive emissions are necessary, they conclude. (Journal of Geophysical Research: Atmospheres, https://doi.org/10.1002/2016JD026070, 2017)
—Emily Underwood, Freelance Writer