KALISPELL, Mont. – Badge and Lander Busse tromped into the forest behind their house on a snowy Sunday in March, their three hunting dogs in tow. It was in these woods, just outside Glacier National Park, that the teenage boys learned to hunt, fish, dress a deer and pick birdshot from Hungarian partridges.

It was also here that the Busse boys grew attuned to the signals of a rapidly warming planet — torrential rains that eroded their hiking trails, wildfires that scarred the land, smoke so thick it forced them indoors.

Watching their cherished wilderness succumb to the effects of climate change enraged the Busse boys, and three years ago they decided to do something about it. Along with 14 other local youth, they joined with an environmental legal group and sued the state.

In their complaint, filed in 2020, the young activists seized on language in the Montana Constitution that guarantees residents "the right to a clean and healthful environment," and stipulates that the state and individuals are responsible for maintaining and improving the environment "for present and future generations."

By virtue of those few words, they argue, Montana's extensive support for fossil fuels like coal, oil and gas is unconstitutional because the resulting pollution is dangerously heating the planet and has robbed them of a healthy environment.

It is a concise but untested legal challenge to a state government that is aggressively defending itself. The trial, which legal experts say is the first involving a constitutional climate case, begins June 12 in Helena, the state capital.

"This is the first that will get into the merits of climate change and what needs to be done, and how the state may have to change its policies," said Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia Law School.

The origins of the case stretch back nearly a decade. In 2011, a nonprofit called Our Children's Trust petitioned the Montana Supreme Court to rule that the state has a duty to address climate change. The court declined to weigh in, effectively telling the group to start in the lower courts.

So the lawyers at Our Children's Trust began building their case. They worked to identify potential plaintiffs. They catalogued the ways in which the state was being affected by climate change. And they documented the state's extensive support for the fossil fuel industry, which includes permitting, subsidies and favorable regulations.

Our Children's Trust, which is largely funded by foundations, has sued state governments on behalf of youth in all 50 states. But Held v. Montana is the first of these cases to head to trial.

"We're really trying to bring the youth generation to the courts, and do so through a human rights lens," said Julia Olson, the attorney who founded Our Children's Trust.

In 2020, Olson once again took aim at Montana, this time with a bigger legal team, a raft of experts and 16 diverse plaintiffs, including the Busse boys.

The oldest plaintiff, Rikki Held, was 18 at the time and grew up on a 7,000-acre ranch in Broadus, where increasingly unpredictable weather has made it difficult for her family to supply water to their property. The youngest plaintiff was Nathaniel K., a 2-year-old boy from Montana City with respiratory problems whose health is threatened by wildfires made worse by climate change, his parents say.

Sariel Sandoval was 17 when the case was filed, and grew up on the Flathead Indian Reservation in northern Montana. She recalled how the huckleberries she once picked early in the summer are now harder to find, and how a lighter snowpack has lowered water levels in Flathead Lake, affecting her tribe's fishing.

"When you have this relationship to the land, it's hard seeing the way climate change is affecting it, the harm that's being done," she said.

For the Busse boys, bucking authority runs in the family. Their father, Ryan Busse, is a former firearms executive who grew disillusioned with the industry and challenged the National Rifle Association. And even though their eighth-grade biology teacher questioned the science of climate change in the classroom, they came to understand that a planet being warmed by fossil fuels was bad news for their backyard.

"A lot of this is just rooted in how many Montanans, including us, live life on an everyday basis, and how ingrained the wildlife and the land and the nature is in who we are," said Lander Busse, who is now 18.

The plaintiffs joined a growing global movement of young people raising the alarm about climate change.

But their activism has come at a social cost. "We can't really openly talk about this case without being flamed by our friends at school," said Badge Busse, 15.

Nevertheless, many of the plaintiffs, including the Busse boys and Sandoval, expect to testify at trial.

In its response to the lawsuit, the state disputed the overwhelming scientific consensus that the burning of fossil fuels was driving climate change and denied that Montana was experiencing increasingly severe weather linked to rising temperatures.

The offices of Montana Gov. Greg Gianforte and state Attorney General Austin Knudsen, both Republicans, declined to comment on the case. "We must focus on American innovation and ingenuity, not costly, expansive government mandates, to address our changing climate," the governor's spokeswoman, Kaitlin Price, said. "The United States must also have an all-of-the-above energy policy, like Montana does, to make our country energy independent and secure again."

No matter who prevails, the case is likely to be appealed to the state Supreme Court. And even if the young Montanans win on appeal, they are not expecting immediate changes.

Rather, the plaintiffs are seeking "declaratory relief." That is, they want the judge to acknowledge that fossil fuels are causing pollution and warming the planet and to declare the state's support for the industry unconstitutional.

Such a judgment would serve another important purpose. Right now, there is barely any case law stating that the burning of fossil fuels is rapidly and dangerously warming the planet. A victory for the Montana youth would help create a foundation for other climate cases. Pennsylvania and New York have similar constitutional guarantees to a healthy environment, and there is a group trying to add them to every state constitution.