Supporters attend a rally Tuesday for a group of young people who filed a lawsuit saying U.S. energy policies are causing climate change and hurting their future. The group faced a major hurdle this week as lawyers for the Trump administration argue to stop the case from moving forward. (Steve DiPaola/AP)

In a courtroom packed with environmental activists, federal judges wrestled Tuesday with whether climate change violates the constitutional rights of young people who have sued the U.S. government over the use of fossil fuels.

A Justice Department attorney warned three judges from the 9th U.S. Circuit Court of Appeals that allowing the case to go to trial would open the doors to more lawsuits.

“This case would have earth-shattering consequences,” Assistant Attorney General Jeffrey Clark said.

He called the lawsuit “a direct attack on the separation of powers” and said the 21 young people who filed it want the courts to direct U.S. energy policy, instead of letting government officials do so.

The young people are pressing the government to stop promoting the use of fossil fuels, saying sources such as coal and oil cause climate change and violate their Fifth Amendment rights to life, liberty and property.

If the case, Juliana v. United States, moves to trial, the judiciary would be “dealing with different branches of government and telling them what to do,” said Judge Andrew Hurwitz, instead of issuing court orders telling officials to stop doing something deemed unconstitutional.

The dire threat to people, particularly the young, demands such action, said Julia Olson, chief legal counsel for Our Children’s Trust, which is representing the plaintiffs, or the people bringing the suit.

“When our great-grandchildren look back on the 21st century, they will see that government-sanctioned climate destruction was the constitutional issue of this century,” Olson told the judges.

The lawsuit asks the courts to declare federal energy policy that contributes to climate change unconstitutional, order the government to quickly phase out carbon dioxide emissions to a certain level by 2100 and mandate a national climate recovery plan.

The Obama and Trump administrations have tried to get the case dismissed since it was filed in Oregon in 2015.

“It’s just really disappointing to see the lengths that they go to — to not only not let us get the remedy that we’re seeking, but not even let us have the chance to prove our facts or present our case at trial,” said Nathan Baring, a 19-year-old from Fairbanks, Alaska, who joined the lawsuit when he was 15.

Lawyers for President Trump’s administration say the young people didn’t find any “historical basis for a fundamental right to a stable climate system or any other constitutional right related to the environment.”

If the 9th Circuit judges decide the lawsuit can move forward, it would go before the U.S. District Court in Eugene, where the case was filed.