A legal decision finding the Australian government owes the country's children protection from harm caused by climate change has been overturned by a court.

The full bench of the Federal Court on Tuesday morning unanimously ruled in favour of an appeal by the Environment Minister Sussan Ley, reversing a decision by a previous judge.

Eight high school students took Ms Ley to court in 2020, seeking to block the expansion of a coal mine that is expected to produce an additional 100 million tonnes of carbon emissions.

Federal Court Justice Mordecai Bromberg in May 2021 knocked back their bid to stop the expansion, but he did rule that Ms Ley has a duty of reasonable care to not cause the children personal injury when exercising her legislative decision-making powers regarding the mine.

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It was lauded as a landmark win that would open an avenue for legal challenges to the government's future decisions on coal projects.

However, Ms Ley soon after announced she would appeal the finding, and on Tuesday the full Federal Court bench - Justices James Allsop, Jonathan Beach and Michael Wheelahan - ruled in her favour.

All agreed a legal duty of care should not be imposed, but the judges varied in their reasons.

Chief Justice James Allsop concluded that decisions about mining approvals belonging to the executive arm of government - ministers of the day - not the judiciary.

Ms Ley also had control over only a tiny contribution to global carbon emissions, he said.

"The lack of proportionality between the tiny increase in risk and lack of control, and the liability for all damaged by heatwaves, bushfires and rising sea levels ... into the future, mean that the duty ... should not be imposed."

Chief Justice Allsop did, however, note the considerable evidence demonstrating the dangers to humanity that climate change presents was not challenged.

"None of the evidence was disputed," he said.

"There was no cross examination of any witness brought by the applicants by those acting for the minister and there was no contrary or qualifying evidence," he said.

Lawyers acting for the group of children now have the option to appeal that decision in the High Court.

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