Citizens affected by climate change are suing the governments of more than 30 European countries in three separate cases before the European Court of Human Rights, alleging that state inaction has violated their human rights.
They are the first such cases to be heard before the Court in Strasbourg, France, and could result in orders for the governments involved to cut carbon dioxide emissions much faster than currently planned.
Here's what you need to know.
What are the three cases?
The first case being heard next Wednesday focuses on the health impact of climate change-induced heatwaves, in a case brought by thousands of elderly Swiss women against the Swiss government as part of a six-year legal battle.
Also on Wednesday, the court will hear a case brought by Damien Carême, a member of the European Parliament for the French Green party, who is challenging France's refusal to take more ambitious climate measures.
The third case, due to be heard after the summer concerns six Portuguese youths, who are taking on 33 countries - including all 27 European Union member states - Britain, Norway, Russia, Switzerland, Turkiye and Ukraine.
They, too, argue those countries have violated their rights and should be ordered to take more ambitious action to address climate change. Six other climate cases are pending.
What rights may have been violated?
The cases will be the first time the court considers on whether climate change policies, if they are too weak, can infringe people's human rights enshrined in the European Convention.
The Swiss women argue that by failing to cut emissions in line with a pathway that limits global warming to 1.5C, Bern violated, among others, their right to life.
The case cites the UN Intergovernmental Panel on Climate Change - which found with very high confidence that women and older adults are among those at highest risk of temperature-related mortality during heatwaves - and uses the applicants' medical records to show their vulnerability.
Carême's application, made in 2019 when he was mayor of the municipality of Grande-Synthe in northern France, will assess whether insufficient government action can amount to a violation of the right to life, by exposing people's homes to climate risk.
In his case, the French Council of State already ordered Paris to take additional measures to cut emissions by 40 percent from 1990 levels by 2030.
Carême will now ask the Strasbourg court to assess whether the government's failure to do more to address climate change violated his right to private and family life.
The Portuguese youths - whose ages range from pre-teens to early 20s - also argue that the 33 countries have failed to agree to curb emissions fast enough to limit global warming to 1.5C.
They argue that their right to life is being threatened by climate change-fuelled impacts like wildfires, and that failure to tackle climate change discriminates against young people who will be hit hardest.
One of the youths was prevented from attending school for days because of the amount of smoke in the air from wildfires, while another of the group's garden was covered in ash.
What's at stake for governments?
The outcome of the cases at the European Court of Human Rights could have wider ripple effects, by either supporting or undermining the prospects of similar cases being won in future - both in national courts, or at the Strasbourg court.
A win could also embolden more activists and citizens to bring similar cases against governments - or, equally, a loss for the claimants could have a chilling effect on potential similar claims.
Some eight countries have piled into the Swiss proceedings as third parties in a move which shows how important the cases are for them.
The 33 governments in the Portuguese case also tried, unsuccessfully, to stop the court from fast-tracking their case.
Some of the countries involved argue that the cases are inadmissible, saying it is not Strasbourg's job to be "supreme court" on environmental matters or enforce climate treaties, in Switzerland's words.
What could the court decide?
The fact that the three cases are all being referred directly to the court's top bench - the “Grand Chamber” - is seen as significant since only cases that raise serious questions about the Convention's interpretation are sent there.
There have already been some cases where national courts have upheld citizens' rights in relation to climate change, most notably the 2019 "Urgenda" case in the Netherlands.
In that case, the Dutch High Court ordered the government to speed up plans to cut greenhouse gas emissions, saying it hadn't done enough to protect its citizens from the dangerous effects of climate change.
The European Court of Human Rights typically deals with cases within three years although it could be faster since at least the Swiss case has priority status.
The Swiss case asks for the court to prescribe deep emissions cuts within three years that would ensure the levels are "net negative" versus 1990 levels by 2030.
A panel of 17 judges will decide on the cases and the outcomes cannot be appealed.