The eco documentary 2040 is a gentle antidote to environmental anxiety. Directed by Damon Gameau, it imagines a world 20 years from now, free from the climate crisis that’s gobbling up our globe. Committed to changing the nihilistic narrative surrounding climate change, Gameau takes his audience on a search for solutions and offers up a message of hope.

As 2040 is released, however, the doom and gloom of the climate crisis Gameau’s documentary takes pains to avoid is inescapable. Australia is ablaze. New South Wales, where he lives with his wife and two children, is experiencing the worst bushfires the country has ever seen. His daughter, to whom 2040 is dedicated, is unable to attend school. For Gameau, the irony of this tragedy stings. “Thousand of school kids were derided for protesting against the very thing that’s now forcing them to miss school,” he says. “People are so frustrated. They’re overwhelmed. They’re angry. Our government is still denying that the fires are climate related. The cognitive dissonance is remarkable.”

Gameau’s frustration at his government’s refusal to acknowledge the climate crisis is noticeably absent from this film. Shifting the focus away from horrific stories of floods and fires, of political ignorance and denial, 2040 is instead a blueprint for the way out of the mess. “There’s been a failure of imagination,” he says. “Instead of constantly beating people over the head with how bad things are, we need to inspire them.”

In 2040, Gameau interviews a host of environmental experts, showing us networks of solar panels, seaweed platforms, the electrification of transport and decentralised energy grids: all solutions to the climate crisis and all of which exist today. Quirky editing has experts perching on toasters, tin roofs and wind turbines as they explain the intricacies of each. It’s unusual and engaging. The message: we must put these ideas into practice if we’re to make any difference.

Gameau says he made 2040 for his daughter’s generation. The film returns repeatedly to warm interviews with children, gently reminding us whose future is at stake. Asked to imagine themselves as adults, kids giggle at the thought of chocolate rain and rocket boots. Climate change is their biggest concern. Unprompted, they speak of hopes of an end to deforestation and dream of “meat grown from a seed”. One imagines an “intergalactic rubbish dimension”. “It’s their future,” Gameau says. “We’ve got to show them there are people who care about that.”

With the success of the school strikes, which has seen more than a million children take to the streets to demand government action on the climate crisis, I ask Gameau if it’s not the kids who need convincing, but the adults. “Kids voices are working,” he says. “People are waking up.” He is determined to use 2040 as a tool for change. It has been projected on to the walls of the UN. A copy of the DVD will be sent to every Australian MP. A screening in the UK parliament is planned for the New Year.

In an effort to reach as many young people as possible, 2040 has been screened free for children in Australia and the Into film festival has rolled out free screenings for schools in England. Delegates to the Youth Climate summit attended a screening in New York. Even singer-songwriter Ellie Goulding has had a private screening.

Could 2040 mark the beginning of the “Greta effect” in documentaries? Gameau thinks so. ‘“Governments, Hollywood, the fossil fuel industry – they’ve always known that film is incredibly powerful,” he says. “We’ve got to be clever and start using the medium for our own benefit.”

With Extinction Rebellion keen to encourage film-makers to focus on the climate crisis, I asked Will Skeaping, co-editor of This Is Not a Drill: An Extinction Rebellion Handbook, how useful he thinks film can be to the cause. “Film-making is vital,” he says. “We need to bring this crisis into all forms of conversation. Film, as the most accessible medium, is one of the best ways to do that.”

Gameau’s documentary shows us there is a way out of the climate crisis. It listens to children, then amplifies their voices. Though the film focuses on the personal changes we can make, Gameau has harnessed the medium to target the political, too. Afterwards, it’s over to us. As Skeaping says: “It’s about getting people out of the cinema and on to the streets.”

• 2040 out now in the UK. A Q&A with Damon Gameau and climate activist Jack Harries is on Friday 22 November at Everyman Broadgate, London EC1.