While there may be broad agreement on the potential benefit of liquefied natural gas in terms of reducing air pollutants, the impact of LNG in terms of greenhouse gas (GHG) emissions has clearly become a point of contention.
Two studies published this year – one out of Cornell University in the US, the other by the World Bank – focused on the use of LNG as a bunker fuel, especially by the ships that transport the product to markets around the globe and point to an emissions issue that can no longer be glossed over, even hidden.
And, it is fugitive methane (CH3), which is a far more pernicious greenhouse gas than carbon dioxide (CO2).
The work carried out by Robert W. Howarth at the Atkinson Center for Sustainability at Cornell is downright damning, while the World Bank study takes a softer approach which admits that methane emissions from the engines of ships burning LNG as a fuel are a greenhouse gas problem that must be eliminated.
Howarth’s core finding is clear. In the US, where shale gas is the primary feedstock, LNG is 33% worse in terms of planet-heating emissions over a 20-year period compared with coal.
“The idea that coal is worse for the climate is mistaken – LNG has a larger greenhouse gas footprint than any other fuel,” says Professor Howarth who, last year, was cited by The New Yorker as “one of the world’s premier methane scientists”.
He is particularly known for his research criticising the presentation of natural gas as a “bridge-fuel” in the transition to renewable energy, a terminology frequently used by Big Oil in the UK, let alone anywhere else, as it seeks to justify continuing with North Sea gas production.
Working with a team of Cornell researchers, Professor Howarth has concluded that natural gas leaves a greenhouse gas footprint that is 33% worse than coal, when processing (to LNG) and shipping are taken into account.
“Natural gas and shale gas are all bad for the climate. Liquefied natural gas (LNG) is worse,” says Professor Howarth, lead author of “The Greenhouse Gas Footprint of Liquefied Natural Gas (LNG) Exported from the United States”.
“LNG is made from shale gas, and to make it you must supercool it to liquid form and then transport it to market in large tankers. That takes energy.”
The emissions of methane and carbon dioxide released during LNG’s extraction, processing, transportation and storage account for approximately half of its total greenhouse gas footprint, Howarth notes.
Over a time frame of 20 years, the carbon footprint for LNG is one-third greater than coal, when analysed using the measurement of global warming potential, which compares the atmospheric impact of different greenhouse gases.
Even on a 100-year time scale – a more forgiving scale than 20 years – the liquefied natural gas carbon footprint equals or still exceeds coal, Howarth warns.
The Cornell findings have implications for LNG production in the US, which has become the world’s largest exporter of the commodity, after it lifted an export ban in 2016, according to the paper.
Exports of LNG doubled between 2019 and 2023, and if allowed by the US government to continue, are predicted to double again over the next four years.
As of 2023, the US is the largest exporter of LNG with a market share of 21%. Australia and Qatar followed in second and third place, with 20% and 19% respectively.
Whereas US exports are shale-based, Australia and Qatar LNG is based on conventional natural gas production.
However, both China and Argentina produce shale gas. The latter is developing its vast shale gas resources from the Vaca Muerta shale formation, which currently ranks as the world’s second-largest shale gas resource.
According to Golar LNG, the project is expected to start LNG exports by 2027, establishing Argentina as an LNG exporter.
China has large shale gas reserves but is developing them for the domestic LNG market. However, commercial production is still limited to the Sichuan Basin.
Back to the US where almost all of the increase in natural gas production since 2005 has come from Texas and Louisiana shales.
Significant methane emissions occur in the natural gas liquefication process, a figure close to 8.8% of the total when using the global warming potential.
Methane emissions from tankers vary from 3.9% to 8.1%, depending on the ship.
The liquefaction process – where the extracted natural gas is cooled to minus 162 degrees Celsius – makes export LNG easier to transport by sea aboard specialist ships of which the current active global fleet stands around 700 vessels with more than 350 more currently on order.
It is estimated that by 2028, all the world’s planned LNG tankers should be in operation. At that point, there would be more LNG tankers in operation than oil VLCCs (very large crude carriers) and ULCCs (ultra-large crude carriers).
There are 772 active VLCCs and ULCCs globally, with a further 200 planned and set to be completed by 2028.
Surprisingly, most modern tankers propelled by multi-fuel two‐and four‐stroke engines have higher total greenhouse gas emissions as a result of using LNG “boil-off” (leakage) from the cargo tanks as a fuel than steam-driven tankers, despite their greater fuel efficiency and lower CO2 emissions, due to methane “slippage” – release of unburned CH3 – in their exhaust.
Methane emissions are largely from the incomplete combustion of LNG fuel by four-cycle and two-cycle tankers, with the release of unburned methane in the exhaust gases.
This adds to the already large footprint of shale gas exploitation and processing into LNG.
Roughly, methane is more than 80 times more harmful to the atmosphere than CO2, so even the relatively small methane slippage from ships can collectively have a sizeable climate impact.
“Almost all the methane emissions occur upstream when you’re extracting the shale gas and liquefying it,” Howarth says. “This is all magnified just to get the liquefied natural gas to market.
“So liquefied natural gas will always have a bigger climate footprint than natural gas, no matter what the assumptions of being a bridge fuel are.
“It still ends up substantially worse than coal.
“Proponents of increased exports of LNG from the US to both Europe and Asia have often claimed a climate benefit, arguing that the alternative would be greater use of coal produced domestically in those regions, with increased emissions of CO2.”
In addition to the methane emissions from upstream and midstream sources before the gas is liquefied to become LNG – and methane slippage from vessels using LNG boil-off as fuel, emissions also occur after regasification and delivery to the final customer.
© Supplied by Cornell UniversityProfessor Howarth warns that there are relatively few measurements of methane slippage and he agrees with others that it should be a priority to further explore slippage rates.
The effect of tanker speed on emissions could also be further explored.
His research has had a major impact on US public policy.
Indeed an early draft of his study was a catalyst to the Biden administration’s pause on new LNG permitting a year ago and which has since been fiercely contested, not least by the Center for LNG whose executive director Charlie Riedl is a critic of the Howarth findings.
Meanwhile, at the World Bank, researchers have come to the view that “the expectation that short- to mid-term use of LNG would provide a significant GHG benefit appears to be questionable.”
Music to the ears of the team at Cornell; but not at Big Oil’s Center for LNG.
They acknowledge that the “unresolved question” of LNG’s lifecycle GHG performance has taken on additional importance with the introduction of the Initial International Maritime Organization (IMO) Strategy on Reduction of GHG Emissions from Ships (known as the “Initial IMO GHG Strategy”).
The Initial IMO GHG strategy commits the industry to achieve a minimum 50 percent reduction in the GHG emissions from the international maritime fleet by 2050 relative to a 2008 baseline (IMO 2018b).
That’s not just LNG tankers but every ship that uses LNG as a fuel, including offshore oil, gas and wind support vessels.
This raises the following question: What role is LNG as a bunker fuel likely to play in the years 2020–2050?
Or more specifically, will LNG play a “transitional,” a “temporary,” or a “limited” role in the sector’s transition toward low- and zero-carbon shipping?
An example of a zero carbon fuel is “green” ammonia, which can be produced using renewably sourced electricity. However, it has drawbacks, including the fact that it is highly toxic and corrosive, even at low concentrations.
Meanwhile, at Norwegian certification body DNV, which considers LNG to be a “mature alternative fuel option,” they are on the methane slippage trail.
Last year, Fabian Kock, head of Environmental Technologies Air at DNV, made it clear that “methane slip is indeed a critical issue for addressing climate change.
“DNV is actively working with many stakeholders and regulators to find pragmatic solutions to overcome this challenge.”
And besides, here in Europe, the shipping sector was incorporated into the EU’s Emissions Trading System (ETS) as of last January and so has environmental footprint obligations.
According to DNV, this expansion will encompass methane and nitrous oxide emissions starting in 2026.
Additionally, the FuelEU Maritime requirements for the GHG intensity of energy utilised on board will come into effect in 2025.
All of which rather puts defensive US naysayers like the Center for LNG out on a limb while the Cornell work led by Prof Howarth appears to be wholly on point.
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