- Why is LNG so popular? -

Global demand for natural gas is expected to rise by 2.5 percent in 2024 to a record level, mostly driven by LNG.

European nations have been big importers to replace Russian gas while Asian nations need it to fuel their growing economies.

Natural gas needs expensive pipelines to be developed from production sites to distribution networks.

Once it is chilled to -163 degrees Celsius however, it liquifies and its volume shrinks by 600 times.

This makes it feasible to transport by special ships and it can then be turned back into gas and injected into existing distribution networks.

- Leaks -

The oil and gas industry often points out that gas-fired power stations emit 2.5 times fewer emissions than their coal counterparts.

Scientists and climate activists say that not only smokestack emissions need to be taken into account, but the entire production and distribution chain.

And that involves a lot of energy for LNG.

"You have to expend so much energy to extract the gas from the ground, to liquefy the gas, to transport it," Rystad Energy analyst Patrick King.

Another problem is the industry is notorious for leaks: from the fields, pipelines and processing facilities. And natural gas is mostly methane, which is much more powerful greenhouse gas than CO2: 86 times as powerful during the first 20 years it is in the atmosphere and 28 times more powerful a century.

"Why lock yourself into another emitter fuel?" said Ana Maria Jaller-Makarewicz, an analyst at the Institute for Energy Economics and Financial Analysis (IEEFA).

"Do the transition directly," she said.

- Variable carbon footprints -

King said LNG produces more emissions than natural gas transported through pipelines.

Some studies indicate that its climate impact could be worse than coal.

A Cornell University study published last month calculated that LNG produced in the United States had a carbon footprint a third higher than coal when production and transport were included, over a 20-year horizon.

Even over a longer period -- 100 years -- its carbon footprint remained the same or higher than that of coal.

But a study by Rystad Energy published earlier this year concluded the opposite. It found that on average, electricity produced with LNG had a lower carbon footprint than carbon when the entire production chain was taken into account.

It also said that even LNG produced in America and shipped across the Pacific to generate electricity could have a carbon footprint just half of the cleanest coal-fired plant.

However, the report did also note considerable differences between different gas fields in reducing methane leaks, which affects their climate impact.

Jonathan Stern, a researcher at the Oxford Institute for Energy Study, said it was extremely complicated to determine whether LNG or coal was worse for the climate.

"It's a subject where you need to be confident that you've got data which is independent and verified," he said.

"And mostly we don't have that data."