University of Waikato law student Sarah Thomson took a similar court case against the NZ government last month. The judge has not announced a decision.

A landmark climate lawsuit against Trump is scheduled for trial next year. Here's what to expect, writes Chelsea Harvey. ​

A trial date has finally been set for a groundbreaking climate-change lawsuit being brought against the United States federal government after multiple hurdles in the past year threatened to prevent it from moving forward. Recently Judge Thomas Coffin ordered that the trial begin February 5, 2018.

The order also permitted three fossil fuel industry trade associations, who had voluntarily joined the case last year as intervening defendants, to withdraw at their own request.

Luke Sharrett Emissions rise from a coal-fired power plant in West Virginia. A lawsuit by American children and young people claims this sort of thing violates their constitutional right to a healthy climate system.

This means the final showdown will take place only between the original plaintiffs and defendants – 21 youths, between ages 9 and 21 – and the federal government, which they claim has violated their constitutional right to a healthy climate system by supporting the production of fossil fuels and emission of greenhouse gases.

While originally filed against the Obama administration, the Trump administration has now assumed the defense by default.

A similar lawsuit in New Zealand pitted Sarah Thomson, of Waikato University, against Environment Minister Paula Bennett over allegedly inadequate climate change action. A decision has not been issued by the judge.

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The case has already come a long way, with the court overturning a number of challenges since it was first filed in 2015. Last November, District Judge Ann Aiken denied motions to dismiss the case filed by the federal government and the intervening fossil fuel industry groups. More recently, she also denied the federal government's request to appeal that decision.

The last possible hurdle the case could face before moving to trial is a final petition filed by the Trump administration this month seeking a rare legal procedure known as a writ of mandamus, which calls for the Court of Appeals for the 9th Circuit to independently step in and review Aiken's original decision to deny the federal government's motion to dismiss the case.

The writ of mandamus is widely considered a kind of hail-Mary petition, one that is rarely invoked and even more rarely granted.

"The United States – in both the previous and current administrations – has endeavoured to bring to an end this improper case that seeks to give one federal court complete control over federal energy policy," said Mark Abueg, a public affairs specialist with the Department of Justice. "We have taken our arguments to the appellate courts."

The decision on whether to allow it now rests with the appeal court. But lead counsel for the plaintiffs Julia Olson, executive director of the advocacy group Our Children's Trust, says it is unlikely to stop the case from moving to trial.

"I would say it would be extraordinary for the 9th Circuit to step in before there's a full factual record in the case," she said.

Assuming that doesn't happen, the trial itself is likely to last about six weeks, according to Olson.

"That's based upon our analysis that we will need three weeks to present our case," she said. " And we're assuming that typically both sides take an equivalent amount of time presenting their cases."

By allowing the case to move to trial at all, the court has acknowledged that the plaintiffs have a legal right to sue the federal government over their constitutional right to a healthy climate system – a right the plaintiffs argue is protected under the public trust doctrine, which holds that the government is responsible for preserving certain essential resources for the public good. In trial, they'll be required to demonstrate the ways in which this right has been violated.

The plaintiffs will present their case in three major components, Olson said. One component will focus mainly on climate science, including the ways in which human activities are altering the Earth's climate and the ways in which these changes are actually harming the plaintiffs. This component will rely largely on expert testimony, Olson said, adding that the plaintiffs have already secured 13 experts for this segment, most of which are scientists.

A second component involves "looking at the historical evidence that we have of what the government knew, when it knew it, what it did with that information – and then also the continuing actions to make climate change worse by the Trump administration," Olson said.

This segment will likely involve the presentation of a variety of federal documents related to the government's knowledge of and action (or inaction) on climate change, as well as testimony from experts and witnesses.

Securing such documents has already been a sticking point. Shortly after the presidential inauguration, the plaintiffs filed a request that the Department of Justice preserve any documents containing information on climate change, energy and carbon emissions or that could otherwise be relevant to the lawsuit.

The Trump administration pushed back against this request in a subsequent motion. This motion was later denied.

A third component of the case may involve a discussion of what can be done to remedy the situation, should the plaintiffs prevail. This section will mainly explore "what are the safe levels of CO2, what's the safe maximum level of warming above pre-industrial levels you can tolerate and so protect the rights of the youth for future generations, what can a solution and remedy look like and what's the feasibility of the remedy to address the harm should the court order a remedy," Olson said.

On the defendants' side, after the plaintiffs have presented their claims, the responsibility shifts to the government to argue that its actions have not violated the plaintiffs' rights. However, the major burden of the case lies with the plaintiffs in actually proving that their constitutional rights have been violated, said James May, a law professor and chief sustainability officer at Widener University, noting that the plaintiffs "have pled a plausible cause of action, but still face an uphill battle."

While the plaintiffs still face an unprecedented challenge in demonstrating that their right to a healthy climate system has been violated – something that has never before been done in federal court – the trial has huge implications regardless of which side prevails, May said.

"Regardless of the outcome, this pioneering lawsuit has altered the global conversation about constitution-based claims for protecting against and responding to climate change," he said. "Such claims have the potential to be instrumental in addressing ineffective, inept, or incongruent national policies. They also represent a beacon of hope for rule-of-law based responses to the biggest challenge humankind has caused, and faced." – Washington Post