Liquefied natural gas (LNG), often touted as a cleaner alternative to coal, has a greenhouse gas footprint 33% larger than coal when factoring in its entire production and shipping process, according to a new Cornell study. The findings challenge the perception of LNG as a “bridge fuel” to cleaner energy.
The study, led by Robert Howarth, professor of ecology and environmental biology at Cornell, was published October 3 in Energy Science & Engineering. It reveals that the process of converting natural gas to its liquefied form for export — including cooling it to minus 260 degrees Fahrenheit and shipping it in large tankers — makes LNG a more harmful contributor to climate change than coal.
“Natural gas and shale gas are all bad for the climate. Liquefied natural gas is worse,” Howarth said. “LNG is made from shale gas, and to make it you must supercool it to liquid form and then transport it to market. That takes energy.”
Methane emissions worsen LNG’s impact
A key factor in LNG’s heavy carbon footprint is methane, a potent greenhouse gas that leaks throughout its production and transportation. Methane emissions, particularly during the liquefication process and from tanker ships, account for nearly half of LNG’s total climate impact, according to the study. While LNG tankers use more efficient two- and four-stroke engines, they still emit methane as exhaust, compounding the problem.
“Methane is more than 80 times more harmful to the atmosphere than carbon dioxide over a 20-year period,” Howarth explained. Even with improvements in fuel efficiency, the leakage of methane during LNG storage and transport means that the greenhouse gas emissions from these ships are higher than those from older steam-powered vessels.
The research found that over a 20-year period, LNG’s carbon footprint is about one-third larger than coal’s. Even when analyzed over a more forgiving 100-year time frame, LNG’s environmental impact is still comparable to, or exceeds, that of coal.
U.S. as a major LNG exporter
The findings come as the U.S. continues to dominate global LNG exports. Since lifting a ban on exports in 2016, the U.S. has become the largest exporter of LNG, with most of the production coming from shale gas fields in Texas and Louisiana.
According to the study, almost all of the increase in U.S. natural gas production since 2005 has come from shale gas, which is then processed into LNG for export. The liquefaction process and methane emissions associated with shale gas extraction further exacerbate LNG’s environmental footprint.
“Almost all the methane emissions occur upstream when you’re extracting the shale gas and liquefying it,” Howarth said. “This is all magnified just to get the liquefied natural gas to market.”
Implications for climate policy
The study’s findings challenge the notion that LNG can serve as a cleaner “bridge” from coal to renewable energy. Howarth argues that despite being labeled a cleaner alternative, LNG’s reliance on methane makes it a more significant contributor to climate change than initially understood.
“So liquefied natural gas will always have a bigger climate footprint than natural gas,” Howarth said. “It still ends up substantially worse than coal.”
The research, supported by the Park Foundation, adds to the growing body of evidence that highlights the need for transitioning away from fossil fuels altogether, rather than relying on LNG as a temporary solution.
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