Photo by Canadian Ice Service.

The LNG industry invariably characterizes LNG as a clean fuel, as if it were identical to domestically produced natural gas that arrives by pipeline. However, the LNG lifecycle adds a significant amount of greenhouse gas emissions above and beyond those produced by domestic natural gas. Significant additional greenhouse gas emissions are generated in the LNG extraction, liquefaction, gasification and transport steps. Depending on the quality of the gas and the distance the LNG must travel, LNG crossing the Pacific may add from 20 to 40 percent more GHG emissions than domestic natural gas. Every segment of the LNG supply chain emits GHGs:

• The liquefaction plants, which are located in the source region of the LNG, use large amounts of energy to generate power and run compressors that chill the natural gas. This uses between 9 and 10 percent of the natural gas being shipped.

• LNG carriers are propelled by marine diesel fuel and LNG boil-off gas, emitting substantial amounts of carbon dioxide along their way, which varies by the distance traveled across the ocean; then the mostly empty ship must return to get more, again burning more fuel. This results in another 7 to 12 percent emissions penalty.

• Production platforms, pipelines, and re-gasification units at the import terminal are all energy-intensive, meaning fuels (mostly natural gas) are converted into carbon dioxide and emitted to the atmosphere.

• Production platforms and gas processing facilities routinely flare some of the throughput gas.

• Natural gas is primarily methane and small amounts of heavier hydrocarbon gases including ethane and propane. When these gases are burned they produce carbon dioxide and water vapor. However, some gas deposits also contain significant amounts of naturally-occurring carbon dioxide. Generally this carbon dioxide is simply vented to the atmosphere, contributing to global warming. Most North American natural gas deposits serving California generally have a low carbon dioxide content of two percent or less. In contrast, Pacific Rim gas fields potentially serving as sources for LNG, specifically in Australia and Indonesia, have high carbon dioxide content, ranging from 10 to 15 percent. This inherent carbon dioxide “debit” further aggravates the climate change implications of importing LNG from these source points when it is vented to the atmosphere.

Throughout the process, methane routinely leaks from gas pipelines, storage tanks, compressors, valves, flanges, and seals; methane is also directly vented from the gas processing plant. While routine leaks and vents are not large in terms of mass flow, methane is a greenhouse gas 23 times more powerful than carbon dioxide per unit. According to one study, the range of natural gas loss through these processes is about 1.4 percent. For the “Pacific Connector” pipeline project PG&E has proposed for Oregon, the natural gas will travel 223 miles before it reaches the California border. The farther the gas must travel, the more chances there are for leakages to occur.

Finally, not all of the methane is fully combusted when gas is burned, and these quantities must also be counted. According to a study of BHP Billiton’s Cabrillo Port project, proposed off the coast of Southern California, (which was vetoed by Governor Arnold Schwarzenegger in May, 2007), all aspects of the project combined (liquefaction, transport, consumption of LNG) would have resulted in approximately 25 million tons of GHGs per year, the equivalent emissions of nearly 5 million cars.

Researchers at Carnegie Mellon University found that worst case greenhouse gas emissions from LNG can be as high as those from the best case integrated gasification combined-cycle (IGCC) coal-fired power plants, when both are measured on a lifecycle emissions basis. The strongest environmental argument for LNG is that it might displace coal, which is considered the worst offender among fossil fuels. But multiple studies demonstrate that the greenhouse gas emissions from LNG rivals that of coal under certain circumstances.

More information on LNG and Global Warming:

Richard Heede - LNG Supply Chain Greenhouse Gas Emissions for the Cabrillo Deepwater Port: Natural Gas from Australia to California 

Carnegie Mellon University - Comparative Life Cycle Air Emissions of Coal, Domestic Natural Gas, LNG, and SNG for Electricity Generation 

RACE – The Climate Impacts of Liquefied Natural Gas

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