As U.S. states look to decarbonize, where they get their natural gas may be an important part of their emissions profiles, according to a recent study.
Calculating the upstream greenhouse gas intensity of each state's gas supplies, researchers at Georgia Tech's School of Civil and Environmental Engineering found that gas consumed in 2018 in the Lower 48 had methane emissions profiles that ranged from 0.9% to 3.6% of the total gas withdrawn that supplied states' consumption.
"It really does make a difference where your natural gas is coming from and what that production leak rate is from your basin," said Diana Burns, the study's lead author who is pursuing a master's degree in environmental engineering at Georgia Tech. "It can be high enough that it makes a big impact on greenhouse gas emissions."
Kansas, Arizona and New Mexico consumed natural gas that emitted over three times more methane during production than most Northeast states in 2018, the study found. Methane, the key component of natural gas, has a shorter atmospheric life than carbon dioxide but has a much stronger warming effect. As a result, researchers and environmentalists have pointed to methane emission reductions, particularly from the oil and gas industry, as an opportunity to help mitigate climate change in the near-term.
Research on methane emissions tends to focus on where the greenhouse gas was released, said Emily Grubert, an assistant professor at Georgia Tech's School of Civil and Environmental Engineering who co-authored the research. But the new study sought to "attribute that to end users to make it a bit more concrete what that actually means at the point of consumption," Grubert said.
"I think what we show is that, a lot like electricity, there is actually pretty variable greenhouse gas intensity associated with the natural gas supply in a way that hasn't really been reflected in those greenhouse gas inventories," Grubert said. "You get to a point where you really do have to think very carefully about methane as we consider decarbonization policies."
States in the Southwest tend to consume natural gas that emits higher levels of methane during production, "largely due to reliance on relatively high-emissions production regions," including the Permian and San Juan basins, according to the study. In contrast, the research found that states in the Northeast consumed natural gas produced in lower methane-emitting regions, including the Marcellus Shale.
The researchers focused solely on production-level methane emissions, applying 2015 emissions rates to 2018 production data.
The industry has launched several voluntary initiatives aimed at curbing methane emissions and has sought to develop technologies to better detect leaks.
"As this analysis shows, production-stage emissions associated with natural gas supplies are sufficiently variable, and estimates of the climate intensity of natural gas used in policy and beyond are sufficiently large, that accurate evaluation and attribution of methane emissions is highly relevant for climate action," according to the study.
However, there are significant uncertainties in quantifying methane emissions given that natural gas production varies year to year due to various impacts, including weather and market effects on the industry, Burns said. Emissions rates can also vary over time and across equipment and systems, the study noted.
"There's a massive amount of uncertainty just in actually deciding how to approach this analytically in addition to the many measurement challenges," Grubert said.