Updated with details from the June 4 court hearing.

The 21 children and young adults suing the federal government over climate change argue that they and their generation are already suffering the consequences of climate change, from worsening allergies and asthma to the health risks and stress that come with hurricanes, wildfires and sea level rise threatening their homes.

With the case back in court on Tuesday, some of the heaviest hitters in the public health arena—including 15 major health organization and two former U.S. surgeons general—have been publicly backing them up.

Today’s children will feel the health impacts of climate change into adulthood if the federal government doesn’t transition away from fossil fuels and reduce greenhouse gas emissions, public health experts wrote in a letter published May 30 in the New England Journal of Medicine (NEJM), echoing a larger court brief signed onto by major health organizations.

“More frequent and longer heat waves, increasing intensity of extreme weather events such as droughts and wildfires, worsening infectious-disease exposures, food and water insecurity, and air pollution from fossil-fuel burning all threaten to destabilize our public health and health care infrastructure,” the authors wrote.

Children and infants are particularly vulnerable to the effects of climate change, as their bodies are still developing, they said. Their respiratory rates are also higher, so particles from fossil fuel burning and ozone take a greater toll. Increasing temperatures contribute to heat stroke risk for children, and can harm babies in utero. And warming temperatures can affect the spread of disease-carrying vectors like ticks, which can transmit Lyme disease, and mosquitoes, which can carry viruses like Zika.

“These are affecting children’s health now, and certainly affecting their future,” said Frederica Perera, a co-author of the letter and the director of the Center for Children’s Environmental Health at Columbia University. “It’s not an abstraction, and not some future threat. It is happening now.”

Researchers are only beginning to understand the magnitude of health issues caused by climate change, said Renee Salas, another co-author of the letter and an emergency medicine physician at Massachusetts General Hospital. “We are just scratching the surface in our understanding of what those health burdens truly are,” she said.

Salas said she hopes the lawsuit and letter “can continue to make climate change personal for people, because health truly is that common denominator that we all share.”

Government’s Climate Duties and Failures

In their lawsuit, Juliana vs. United States, the children and young adults accuse the federal government of violating their constitutional rights by failing to take action on climate change and continuing to promote and subsidize fossil fuels.

The lawsuit is based on the public trust doctrine, a legal concept that the government holds resources such as land, water or fisheries in trust for its citizens. Climate litigators contend that the government is a trustee of the atmosphere, too, and the young plaintiffs argue that the government abrogated its duty to limit fossil fuel use and cut greenhouse gas emissions, despite knowledge for decades that combustion of fossil fuels adds carbon dioxide to the atmosphere and changes the climate. 

The federal government has fought the case at every turn and has tried repeatedly to get it dismissed, which led to this latest hearing.

On Tuesday, a three-judge panel of the U.S. Court of Appeals for the Ninth Circuit heard the two sides’ arguments, which the judges will now consider as they weigh whether the case will be allowed to move forward.

The children’s lawyer, Julia Olson from Our Children’s Trust, faced off against U.S. Assistant Attorney General Jeffrey Bossert Clark, a Trump administration appointee who represented the oil giant BP in lawsuits over the nation’s largest oil spill and has repeatedly challenged the science of climate change. So far, the government’s lawyers haven’t contested the argument that climate change is harming the plaintiffs. Instead, they have said the federal government is not responsible and have focused on arguments that the court doesn’t have the authority to order the political branches to act.

During the hearing, the judges asked tough questions of both sides. The Supreme Court had warned the appeals court to tread carefully in the highly unusual and potentially precedent-setting case, and the judges were doing so.

“You present compelling evidence that we have a real problem,” Judge Andrew Hurwitz told Olson. “You present compelling evidence that we have inaction by the other two branches of government. It may even rise to the level of criminal neglect. The tough question for me, and I suspect for my colleagues, is do we get to act because of that.”

“You’re arguing for us to break new ground,” the judge said.

Clark, arguing for the government, told the judges that a ruling for the plaintiffs would be “a dagger at the separation of powers.”

Olson focused on the children’s constitutional rights to life and personal security, saying future generations would look back and see that “government-sanctioned climate disruption was the constitutional issue of this century.”

The plaintiffs are calling for sweeping changes in federal climate efforts and in government programs that subsidize or foster the development of fossil fuels. The trial, if allowed to proceed, could bring to light decades of federal policy on fossil fuels and climate change—including information previously unknown to the public.

‘They Were Born Into This Problem’

The NEJM letter echoed an amicus brief filed in support of the young plaintiffs’ lawsuit by nearly 80 physicians and researchers and 15 health organizations, including the American Academy of Pediatrics, the American Heart Association and the Infectious Diseases Society of America.

“There’s a really robust body of scientific literature that supports each of these different kinds of health impacts that are already being observed and are projected to get worse and worse,” said Shaun Goho, deputy director of the Emmett Environmental Law & Policy Clinic at Harvard Law School and one of the attorneys who filed the amicus brief.

“The Juliana generation is going to feel and suffer from those impacts in a way that’s really different and more extreme than what any previous generation has felt,” Goho said.

Two former U.S. surgeons general also weighed in, publishing an op-ed in The New York Times on Monday. Drs. Richard Carmona and David Satcher warned about several effects of climate change on health, from cognitive impairments due to malnutrition to lost school days and mental health concerns.

“The country has eliminated polio, reduced cancer death rates and raised life expectancy over time,” they wrote. “Now, as the country faces the potentially catastrophic consequences of climate change, the country needs to understand the public health implications of a warming climate.”

The former surgeons general, like the NEJM letter, pointed out that children inherited the changing climate that threatens their future.

“They were born into this problem; they did not create it,” they wrote. “They are uniquely vulnerable: their developing bodies suffer disproportionately from climate change’s most serious and deadly harms.”