The greenhouse gas footprint of using liquified natural gas (LNG) exported from the US could be greater, in certain circumstances, than that of burning coal, according to a new study.
LNG exports from the US have risen rapidly since a ban on its export was lifted in 2016: the US is now the world's largest exporter.
That LNG is produced largely from shale gas, which is extracted using high volume hydraulic fracturing – fracking - and high-precision directional drilling.
Supporters of increased exports have argued that the alternative to exporting LNG would be greater use of coal, which would mean increased emissions of carbon dioxide. But despite this, in January 2024, U.S. President Biden placed a moratorium on increasing exports of LNG pending further study of the environmental impacts.
And now a peer-reviewed paper, The greenhouse gas footprint of liquefied natural gas exported from the United States, by Robert Howarth at Cornell University, has calculated that the overall greenhouse gas footprint for LNG as a fuel source could be 33% greater than that for coal when looking at its 20 year global warming potential (GWP20).
“Even considered on the time frame of 100 years after emission…which severely understates the climatic damage of methane, the LNG footprint equals or exceeds that of coal,” the research says.
An early version of Howarth’s paper was used by the White House as evidence for the need for greater study on the greenhouse gas emissions from LNG, particularly methane emissions.
The paper is published in the journal Energy Science & Engineering.
“With an even greater greenhouse gas footprint than natural gas, ending the use of LNG should be a global priority. I see no need for LNG as an interim energy source and note that switching from coal to LNG requires massive infrastructure expenditures, for ships and liquefaction plants and the pipelines that supply them. A far better approach is to use financial resources to build a fossil-fuel-free future as rapidly as possible,” Howarth says in the paper.
The paper notes that production of shale gas, as well as liquefaction to make LNG and its transportation by tanker, is energy-intensive, all of which adds to the LNG greenhouse gas footprint. On top of this, the production and transport of shale gas emits a substantial amount of methane, and liquefaction and tanker transport of LNG can further increase methane emissions.
Carbon dioxide (CO2) from end-use combustion of LNG accounts for only 34% of the total LNG greenhouse gas footprint, when CO2 and methane are compared over 20 years global warming potential following emission.
According to the research, it is the upstream and midstream methane emissions that are the largest contributors to the LNG footprint. Adding CO2 emissions from the energy used to produce LNG, total upstream and midstream emissions make up on average 47% of the total greenhouse gas footprint of LNG.
Other significant sources of emissions are the liquefaction process (8.8% of the total) and tanker transport (5.5% of the total). “Even though carbon dioxide emissions are greater from burning coal than from burning natural gas, methane emissions can more than offset this difference.
As a greenhouse gas, methane is more than 80 times more powerful than carbon dioxide when considered over a 20-year period, and so even small methane emissions can have a large climate impact,” the paper says.
Using domestic natural gas in the US for electricity production (but not as LNG) has a greenhouse gas footprint very similar to that of coal, the paper says, noting that neither natural gas nor coal used domestically in the US has a large climate advantage over the other.
But the footprint for exported LNG is greater than that of coal, diesel oil, or natural gas even in the case of the shortest trips for the tankers. The greenhouse gas footprint for LNG is 28% greater than that of coal for the shortest cruises and 46% greater for the longest cruises.
By far the heating option with the lowest greenhouse gas impact is the use of a ground-source heat pump.
Not everyone is convinced: some have argued with the details of Howarth’s analysis and have said that restricting LNG supply does not necessarily represent an effective decarbonization strategy because it may cause some countries to shift their energy policy in favour of domestic coal. Republicans in Congress have also been critical of the ban on LNG. And other studies have reported that total LNG emissions are lower, but Howarth says this is because they use lower estimates for upstream and midstream emissions of methane - which are themselves based on unverified self-reporting from the oil and gas industry.
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