A clutch of high-profile legal cases over responsibility for the effects of climate change will be fought out in courtrooms next year as claims stack up against both governments and some of the world's biggest oil and energy companies.
Lawsuits in the United States brought by young activists and several Californian cities are most likely to make waves, but legal action by a Peruvian farmer in Germany and Greenpeace in Norway could also cause ripples, said lawyers and academics.
"There is a trend towards more litigation around climate change, and probably the lack of political action in the United States may increase that trend," said Sophie Marjanac, a London-based lawyer at non-profit environmental law group ClientEarth.
"Where there's an abdication of leadership on climate action, I think the courts will have a greater role to play," she told the Thomson Reuters Foundation.
Lawyers and campaigners are closely watching the looming legal battles they say could set the stage for fresh claims against major oil and industrial companies, and pressure governments to ramp up action on climate change.
With US President Donald Trump and his cabinet members named as defendants, the Juliana v. United States case brought by 21 young activists from Oregon is set to be one of the most closely followed in 2018.
In the federal case, scheduled for trial in February, the plaintiffs hope to establish that the government's climate change policies have failed to protect their constitutional right to live in a habitable environment.
The case remains locked in legal limbo, however, as the government tries to block it from proceeding.
Lawyers and academics say Juliana builds on the groundbreaking Urgenda case brought by hundreds of Dutch citizens in 2015, which saw the government ordered by a district court to accelerate reductions of greenhouse gas emissions.
However, that outcome is now being appealed, with a decision likely early next year.
Elsewhere, a January judgment is expected in a case brought by Greenpeace Nordic and environmental group Nature and Youth against Norway, which they claim has breached its pledge to combat climate change by granting oil and gas exploration rights.
HISTORY REPEATING?
Some lawyers and researchers say claims seeking specific damages from energy and industrial companies for actions that may have contributed to climate change could have a bigger impact than constitutional cases.
A successful ruling against a heavyweight corporate could potentially unleash a wave of similar claims, say case watchers, who reference long-running fights against tobacco, asbestos and pesticide manufacturers over harm to human health.
At least seven Californian cities and counties have brought lawsuits against major fossil fuel companies. San Francisco and Oakland are seeking billions of dollars to help protect against rising sea levels they blame on climate change.
"Why should taxpayers and impacted communities alone bear the growing costs of climate impacts when fossil fuel companies have played an outsized role in making the problem worse?" said Peter Frumhoff, director of science and policy at the Union of Concerned Scientists, after Santa Cruz city and county both filed lawsuits this month.
Tracy Hester, a lecturer at the University of Houston Law Center, said such claims could "redefine the rules of the game". "They're essentially not trying to bring a global claim that's going to lock up all these issues in one court... they're different in that they're seeking damages," he said.
Trump's move to pull out of the Paris climate change accord and roll back environmental regulations means campaigners are increasingly resorting to litigation, as they did under former President George W. Bush, said case watchers.
MITIGATION NOT LITIGATION
While climate-related suits are not new, scientific advances could bolster plaintiffs as they try to pin responsibility for climate change on particular polluters.
A German court has agreed to hear evidence in a case brought by Peruvian farmer Saúl Luciano Lliuya against RWE AG, asking the power giant to pay to reinforce a lake above his village dangerously swollen by glacial melt he says is caused by global warming the company contributed to.
Yet while there has been a steady rise in cases seeking to hold corporations and governments to account, few make it to court and legal action is largely limited to richer countries.
Despite a few exceptions - including a farmer who successfully sued Pakistan's government in 2015 - mitigating rather than litigating against climate change is favoured in poorer countries where legal success is less likely, according to Cosmin Corendea, a legal expert at the United Nations University in Bonn.
But the knock-on effect of rulings on companies and governments could eventually be felt around the world, including in countries already struggling with climate change impacts.
"The decision of the court echoes," said Corendea. "It's important in climate change litigation to have this kind of momentum."
FACTFILE: THE CASES TO WATCH
Climate change cases numbered nearly 900 in 24 nations as of March, according to a survey by UN Environment and Columbia Law School, marking a steady increase in lawsuits filed to hold governments and companies to account over carbon pollution.
- URGENDA FOUNDATION V. KINGDOM OF THE NETHERLANDS (NETHERLANDS)
This landmark case energized the climate movement in 2015 when a district court sided with the nearly 900 Dutch citizens behind it, ordering their government to cut greenhouse has emissions faster.
It was "one of the most important climate change decisions ever issued", said Michael Gerrard, director of Columbia Law School's Sabin Center for Climate Change Law in New York.
But the outcome is now being appealed and a decision could be handed down as early as 2018, said Gerrard.
The Urgenda ruling remains the only one of its kind globally to declare a government's obligation to control climate change.
It did so by citing the Dutch constitution, prompting a flurry of similar complaints worldwide where plaintiffs are trying to enlist their nations' founding principles to curb global warming.
- JULIANA V. UNITED STATES (UNITED STATES)
Trial in this federal suit filed by a group of 21 US teenagers could begin in February 2018.
Building on the precedent established by the Urgenda case, the young people from Oregon charge their government's climate policy is inadequate and flouts their constitutional right to live in a habitable atmosphere.
The case is currently stalled amid efforts by the US government - fearful it will lead to a constitutional crisis - to prevent it going forward.
"It's clearly a case to watch," said Sean Hecht, co-executive director of the Emmett Institute on Climate Change and the Environment at UCLA in California.
"It would be extraordinary for a judge to take the step of holding the U.S. government responsible for this, but it's not unthinkable," he told the Thomson Reuters Foundation.
- LLIUYA V. RWE (GERMANY)
A Peruvian farmer, Saúl Luciano Lliuya, is seeking $20,000 in damages from a large German energy utility based half-way around the world.
Lliuya argues that RWE AG holds some responsibility - by emitting planet-warming gases - for the melting of glaciers and rising water level of a lake near his Andean town.
Observers are calling the Lliuya suit, which is due to hear evidence in 2018, a test case of whether a company can be held financially liable for its contribution to the effects of climate change in other parts of the world.
- EXXON MOBIL CORPORATION V. MAURA TRACY HEALEY (UNITED STATES)
Exxon Mobil is battling attorney generals in Massachusetts and New York who are investigating the oil giant, after news reports charged in 2015 that its own scientists had found cutting fossil fuel use was needed to slow down climate change.
Exxon's case against Massachusetts' attorney general Maura Healey and a similar one against her New York counterpart seek to derail subpoenas to obtain the company's internal documents on climate science.
"There's a lot at stake because these companies are very concerned about potential liability," said UCLA's Hecht.
- GREENPEACE NORDIC V. GOVERNMENT OF NORWAY (NORWAY)
In another case rooted in a constitutional argument, this lawsuit charges that Norway violated the country's constitution by letting energy firms explore for oil and gas in the Arctic Barents Sea.
With a judgment expected in January, a win by Greenpeace would "re-energise similar litigations in other countries", said Columbia Law School's Gerrard.