The proceedings, which opened at the European Court of Human Rights (ECHR) in Strasbourg on Wednesday, are the largest climate change case ever heard by the court.

The six activists - aged between 11 and 24 - have filed the case against the 27 EU member states as well as the United Kingdom, Switzerland, Norway, Russia and Turkey.

"Today we will stand up at the ECHR to argue for our rights and our future," the applicants, who are all attending the hearing in person, wrote on social media.

Should the six be successful, member countries could be forced to speed up their efforts to tackle climate change.

"This is truly a David and Goliath case," said Gearóid Ó Cuinn, the director of the UK-based non-profit organisation Global Legal Action Network (GLAN) that's been supporting the group.

"It is unprecedented in its scale and its consequences," he said.

The court's rulings are legally binding and failure to comply makes members liable for hefty fines.

Legal 'game-changer'

"This judgment would act like a binding treaty imposed by the court on the respondents, requiring them to rapidly accelerate their climate mitigation efforts," GLAN lawyer Gerry Liston said.

He added: "In legal terms, it would be a game-changer."

Mr Liston said it would also act as a precedent for future climate cases by providing guidance to national courts.

"We've put forward evidence to show that it's within the power of states to do vastly more to adjust their emissions, and they are choosing not do it," he added.

The applicants say the failure to adequately address human-caused climate change violates their rights, including the right to life, and damages both their physical and psychological well-being.

"Without urgent action to cut emissions, [the place] where I live will soon become an unbearable furnace," applicant, Martim Agostinho, 20, said in a statement.

The group started legal proceedings following a series of deadly wildfires in central Portugal - where four of them live - in 2017 in which more than 100 people were killed.

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'We're rooting for you'

To succeed, the six will need to prove they have been sufficiently affected by climate change to be considered victims - a claim legal teams for the 32 nations dispute.

They will also need to convince the court that governments have a legal duty to make sure global warming is held to a 1.5C increase since pre-industrial times - in line with the goals of the 2015 Paris climate agreement.

They were supported by a group of people of all ages who gathered outside the court with banners reading "Stand with youth" and "We are rooting for you".

Dozens of lawyers are defending the 32 countries - versus six representing the applicants.

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Mr Liston described it as a hearing on an "unprecedented scale."

Taking on the legal teams of over 30 very well-resourced countries would not be easy, he added.

As well as questioning the claim that the plaintiffs are victims of climate change harm, lawyers for the 32 nations are also disputing the admissibility of the case.

Barrister Sudhanshu Swaroop, a counsel for the UK, said the group should have gone through national courts first and stressed that since they are not nationals of 31 of the countries they are attacking, the ECHR doesn't have jurisdiction.

Climate litigation is growing internationally.

Last month young environmentalists won a similar case in Montana, in the US.

Two other climate change cases are pending for the ECHR's grand chamber.

A ruling is expected in the first half of 2024.

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