A federal appeals court has ruled in favour of 21 teenagers suing the US government for its energy and climate change policies.

The case, Juliana v. United States, will now be able to go to trial as President Donald Trump’s administration is expected to try and get the Supreme Court to throw out the case.

The lawsuit alleges that decades of US energy policy takes away the children’s Constitutional right to “life, liberty, and the pursuit of happiness”.

The complaint claimed that US energy policy over the last 50 years in promoting the use of fossil fuels and becoming one of the world’s largest polluters has put these young people’s lives in jeopardy now and spoiled the environment for future generations.

But, the new federal appeals court ruling defeated the current US Department of Justice’s request that the case be thrown out on the basis that it is based on “utterly unprecedented legal theories”.

The Trump administration also argued that “it’s unreasonable to delve into “unbounded” research into the executive branch dating back to the Lyndon Johnson presidency,” as Bloomberg News reported.

Mr Trump himself has repeatedly called climate change a "hoax" perpetrated by the Chinese.

The case, supported by Our Children’s Trust legal organisation in Eugene, Oregon, was first fought by former President Barack Obama’s administration in 2016.

Julia Olson, the attorney representing the group of teenagers, told The Independent that though Mr Obama “acknowledged climate science and that we are in a dangerous situation, but his actions did not match his speeches”.

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She said that the administration “promoted and supported fossil fuels as much as George W. Bush before him. His signature “climate policy”, the Clean Power Plan (CPP) would have replaced coal with natural gas and basically flatlined US emissions through 2040 according to the US Department of Energy’s projections, leading to climate catastrophe”.

The Trump administration’s Environmental Protection Agency (EPA) head Scott Pruitt made it his mission to dismantle the CPP, legislation meant to address the fact that power plants account for almost 40 per cent of the country’s emissions.

If left in place, the CPP would have reduced power plants’ carbon emissions by 2030 to a level 32 per cent lower than they were in 2005.

But now, Ms Olson said they have “the green light for trial,” adding that the group will request a trial date later this year.

US District Judge Ann Aiken is now deciding which of the several federal agency officials can be questioned in depositions.

Among those named are Mr Pruitt, Energy Secretary Rick Perry, Budget Director Mick Mulvaney, Ryan Zinke the Interior Secretary, Senator Mitch McConnell’s wife Transportation chief Elaine Chao, Defence Secretary James Mattis, and Mr Trump himself.

The teenagers had earlier requested Secretary of State Rex Tillerson, a former CEO of oil and gas giant ExxonMobil, to testify but the request was denied whilst he was going through the Senate confirmation process for his current position.

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Ms Olson underscored the importance of the case to American children in particular and why this has become a court case to impose against the US government rather than only a social movement.

She said the federal government has “consistently discriminate[d] against children in making climate and energy policy”.

In June 2017, Mr Trump began the withdrawal process for the US to cut ties with the Paris Agreement, signed by nearly 200 countries in an effort to curb global carbon emissions and contain global warming to 2 C.

There was immediate and widespread criticism of the move from world and local leaders and CEOs alike.

More than a thousand mayors and CEOs joined in the ‘We Are Still In’ coalition to say they will still work to meet the targets laid out for the US in the Paris accord despite the Trump’s administration’s decision.

Though the group has gotten some support from “a handful” of mayors and cities, Ms Olson said the Trump administration is leading the country to “climate catastrophe”.

“Remember that the US is a primary reason that the international targets, including those in the Paris Agreement, are not binding and are not based in the science of stabilising our climate system and saving our ice sheets,” Ms Olson cautioned.