LNG HAS A HIGHER CARBON CONTENT THAN COAL

According to a new study from Cornell University, liquefied natural gas leaves a 33% higher greenhouse gas footprint than coal when processing and transportation are considered. The work was published in the journal Energy Science & Engineering.

“Natural gas and shale gas are all bad for the climate. Liquefied natural gas (LNG) is even worse,” says Robert Howarth, study author and professor of environmental science. “LNG is made from shale gas, and to produce it, it has to be supercooled into a liquid state and then transported to market in large tankers. That takes energy.”

Methane and carbon dioxide emissions from extraction, processing, transportation and storage account for about half of the total greenhouse gas footprint, Howarth said.

Over 20 years, LNG’s carbon footprint is a third larger than coal’s when analyzed using a global warming potential measure that compares the atmospheric impact of different greenhouse gases. “Even on a 100-year time scale — a more lenient 20-year time scale — LNG’s carbon footprint is equal to or greater than coal’s,” Howarth said.

The liquefaction process, when extracted natural gas is cooled to minus 127 degrees Celsius, makes LNG easier to transport on tankers. But this method of transportation comes with environmental costs. Ships with two- and four-stroke engines that carry LNG have lower carbon dioxide emissions than ships with steam engines. But when ships with such engines burn LNG during storage and transport, the methane escapes into the atmosphere as exhaust gas, causing emissions to rise.

“Methane is 80 times more harmful to the atmosphere than carbon dioxide, so even small emissions can have a big impact on the climate,” Howarth said. This is why modern two- and four-stroke tankers produce more greenhouse gas emissions than steam-powered tankers. Despite their greater fuel efficiency and lower carbon dioxide emissions, methane is still released in tanker exhaust.

Significant methane emissions occur during the liquefaction of natural gas: almost 8.8% of total emissions when global warming potential is taken into account. Methane emissions from tankers range from 3.9 to 8.1% depending on the vessel.

“Almost all the methane emissions happen first, when you extract the shale gas and liquefy it,” Howarth says. “All of that is just to get the LNG to market.”

“Therefore, LNG will always have a greater climate impact than natural gas, regardless of whether it is a transition fuel. It will still ultimately turn out to be significantly worse than coal,” the scientists concluded.