“Earth Emergency,” a documentary by Massachusetts filmmakers about saving the planet, hasn’t been screened yet in the United States. It premieres nationwide on PBS stations on Dec. 29.

But it’s already made a global impact.

The film is narrated by Richard Gere and features cameos by the Dalai Lama and Greta Thunberg. It was screened in Glasgow during the 2021 United Nations Climate Change Conference at an event hosted by Prince Charles. It was uploaded on the International Space Station for astronauts to see, and watched by members of the UK Parliament at a special screening and panel. A book about the film will be published in 2022 by Penguin Random House.

“This is really gratifying for me,” said Melanie Wallace of Newton, the film’s impact producer and the longtime former series producer for “NOVA,” the PBS science series.

Wallace is one of two Jewish members of the production team, the other being senior producer and writer Bonnie Waltch of Watertown. Susan Gray of Swann Street Films in Rowley directed the film.

While climate change is finally being widely accepted as the existential crisis of our time, there’s a critically important aspect of it – the role played by environmental feedback loops – that’s not been generally understood, let alone talked about. Feedback loops are the focus of the film, which documents the surprising and alarming way in which the Earth is essentially warming itself.

It’s well-known that fossil fuel emissions from human activity are driving up the Earth’s temperature. But it’s not just emissions heating up the globe, as the documentary makes clear through interviews with top climate scientists. The rising temperatures are setting in motion the planet’s own natural warming mechanisms – irreversible chain reactions – which then feed upon themselves, amplifying and accelerating the process of warming the earth.

Scientists have identified dozens of feedback loops already in motion. The film concentrates on four of them, including the melting of sea ice in the Arctic Ocean, and increased droughts and fires in forests.

“Each amplifies warming, and combined, they are spinning out of control,” the film’s narrator ominously warms us. (The film does end on a somewhat hopeful note, though, with Thunberg, the young Swedish climate activist, urging viewers to take action. “Every great change throughout history has come from the people,” she says. “We can start the change right now.”)

Neither Wallace nor Waltch was familiar with feedback loops before they began working on the film, although “scientists are very concerned about it,” Wallace said. “They’re tearing their hair out over it.”

Several of these scientists, as we see in the film, are from Massachusetts, including George Woodwell, who founded the Woods Hole Research Center in 1985 (Now the Woodwell Climate Research Center). Woodwell has been sounding this alarm for 50 years: In 1989, he predicted in a Scientific American article that “the warming, rapid now, may become even more rapid as a result of the warming itself.”

Thirty years later, Thunberg echoed these warnings. “But even though Greta talked about them, it wasn’t part of the public conversation,” said Waltch.

The filmmakers started out by making a series of five short films about feedback loops, working with Northern Light Productions in Boston. “We thought they’d have a better chance of being seen [if they were short], and educators could use them,” said Waltch.

The official launch was in January 2021 with a virtual discussion between climate scientists, the Dalai Lama, and Thunberg. More than a million viewers tuned in. In March, the Smithsonian National Museum of Natural History hosted a webinar featuring the short films.

Heartened by the strong interest, the filmmakers decided to consolidate them into a one-hour film, with the help of Warehouse 51 Productions in the UK. Through contacts Wallace had developed over years working at “NOVA,” they reached out to the Prince of Wales, a dedicated environmentalist who had recently unveiled the Terra Carta – a sustainability plan for the private sector.

A few months later, the filmmakers got an email back from the “Household of The Prince of Wales & the Duchess of Cornwall.”

“[His Royal Highness] will be hosting the Terra Carta Action Forum” in November in Glasgow, it said. “We would be delighted to host a screening of Earth Emergency.” The film team went and met Prince Charles.

It’s been a heady experience, but the filmmakers are hoping the film will facilitate change. “My hope is that policy makers will understand better the urgency of doing something,” said Waltch. “Nothing seems to have gotten through loudly enough to make people act in a timely manner. We hope learning about feedback loops will send a more urgent message to policy makers and corporations to start turning the ship around. Or stop it from getting worse.”

“One of the key tenets of Judaism that resonates with me is about repairing the world,” said Wallace. “I think this is the time in our lives when focusing on climate change is the essential element of how to be a responsible person in this world.”

“Earth Emergency” will air on WGBH on Wednesday, Dec. 29, at 8 p.m. For information about the film, visit pbs.org/show/earth-emergency/