NEW YORK-A group of American students, one as young as nine, is suing President Donald Trump over the U.S. government's climate-change policy that they claim puts their future in jeopardy, their attorney said on Friday, Feb. 10.

Trump has expressed doubts about the science behind climate change and has vowed to revive the oil, gas and coal industries.

His policies have his administration on a collision course with an overwhelming majority of scientists who believe that human consumption of fossil fuels is warming the planet and triggering sea level rise and more frequent powerful storms.

The 21 students added Trump as a party to their two-year-old case in order for litigation to continue under the new administration, said lead counsel for the plaintiffs, Julia Olson. Trump replaces former President Barack Obama as a named party in the case against the U.S. federal government.

While the substitution may be procedural, the young people said they had been spurred on by Trump's expressions of doubt about the science behind climate change.

"I am hopeful that our case will reverse or prevent all damage our current president may inflict," Aji Piper, 16, from Seattle, one of those filing the suit, said in a statement.

The lawsuit, filed in an Oregon federal court in 2015, alleges that the government's response to climate change has been slow and violates the constitutional rights of the young plaintiffs-who range in age from nine to 20.

The suit claims the United States and various executive agencies have known for more than 50 years that carbon dioxide from burning fossil fuels was destabilizing the climate system and significantly endangering them.

"The U.S. is most responsible for climate change so it's really the most important case in the world right now on the issue," Olson told the Thomson Reuters Foundation by phone.

A defense attorney with the U.S. Department of Justice said by email that he was not authorized to comment on the case.

Trump, a Republican who took power on Jan. 20, has dismissed global warming as a hoax created by China.

His nomination of Oklahoma Attorney General Scott Pruitt, who has expressed doubt about climate change science, to head the U.S. Environmental Protection Agency has further alarmed climate advocates.

The naming of Trump in the case sent a strong a political message, said Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia University in New York City.

"It has the symbolic effect of targeting the individual who has lately become the biggest obstacle to the U.S.'s action fighting climate change," he said.

The trial could begin later this year, Olson said.