The EDO dubbed it a "once in a generation case" as it was the first time an Australian court had heard expert evidence about the urgent need to stay within a global carbon budget in the context of a proposed new coal mine.

Justice Preston noted the "significant adverse social impacts on the community" from the proposed mine but - in a court-first in Australia - highlighted the climate impacts of coal mining.

"The construction and operation of the mine, and the transportation and combustion of the coal from the mine, will result in the emission of greenhouse gases, which will contribute to climate change," Justice Preston said in his judgement.

Di Montague, a member of Groundswell Gloucester, told fellow anti-mine campaigners, "we've won, we've won". The result should "reverberate across every community fighting coal and coal seam gas in Australia", Ms Montague told the Sydney Morning Herald ahead of the result.

"It's a very strong judgement," David Morris, EDO NSW's chief executive, said after the judgement was released to a packed court room.

Planning Minister Anthony Roberts declined to comment on the judgement's wider importance, saying only: "That’s the legal process and we respect the court’s decision”.

Comment has been sought from Gloucester Resources and the NSW Minerals Council.

The result was being watched with interest internationally. Climate litigation, particularly in the US and European nations such as the Netherlands, is growing as climate campaigners frustrated by insufficient political action seek alternative routes to cutting greenhouse gas emissions.

Will Steffen, an adjunct professor at the Australian National University who gave evidence in court about the climate impacts of coal, welcomed the result.

"It is absolutely clear that the Paris climate targets cannot be met if we continue to open up new fossil fuel reserves," Professor Steffen said.

"This landmark decision sends a clear message to the fossil fuel industry that it cannot continue to expand if we are serious about tackling climate change."

"Shutting the door on new fossil fuel developments will be a major turning point in the battle to stabilise the climate system - and will add further momentum to the shift to clean, reliable renewable energy systems," he said.

'All emissions contribute'

Justice Preston elaborated on his judgement, noting that "all of the direct and indirect greenhouse gas emissons of the Rocky Hill Coal Project will impact on the environment".

"All anthropogenic greenhouse gas emissions contribute to climate change," he said.

In aggregate, the mine would have contributed 37.8 million tonnes of carbon-dioxide equivalent, "a sizeable individual source" of such emissions, Justice Preston concluded.

"It matters not that the aggregate of the Project's greenhouse gas emissions may represent a small fraction of the global total", he said. "The global problem of climate change needs to be addressed by multiple local actions to mitigate emissions by sources and remove greenhouse gases by sinks."

In summarising, Justice Preston said an open-cut coal mine in "this part of the Gloucester valley would be in the wrong place at the wrong time".

It was the wrong place because of "this scenic and cultural landscape", including indigenous ones, and its proximity to home.

However, it was also the "wrong time because the greenhouse gas emissions of the coal mine and its coal product will increase global total concentrations of [those gases] at a time when what is now urgently needed, in order to meet generally agreed cimate targets is a rapid and deep decrease" in those emissions, Justice Preston concluded.

Such a judgement "will be generally applicable to any coal mine in Australia", Mr Morris from the EDO said.

The town of Gloucester and its campaigners are no strangers to the spotlight.

Groundswell Gloucester successfully saw off energy giant AGL and its plans to develop at least 330 coal seam gas wells in the valley, with the anniversary of that result three years ago last Monday.

More to come