The director and star of a film about one of the scientists who proved the contribution of greenhouse gases to global warming have urged audiences and movie-makers to recognise the urgency of action required – a message which has found echoes throughout the festival

The Cannes film festival has ended with a question: “Now you know, what are you going to do about it?” Such are the final words of the closing night film, Ice and the Sky, which implores its audience to recognise the urgency of action required on climate change.

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The documentary wrapped up the 68th edition by foregrounding an issue so central this year it overshadowed even the debate over whether high heels should be compulsory at premieres.

Ice and the Sky, directed by The March of the Penguins’ Luc Jacquet, is a study of French glaciologist Claude Lorius, whose Antarctic research placed beyond contest the role of man in global warming.

Jacquet declared himself “impressed” Cannes had given his movie such a prominent spot in the schedule. “Showing this film in the world’s largest film festival is contributing to highlighting this huge challenge facing humanity as quickly as possible to secure its future and the future of the planet,” he said.

The director said that it was the responsibility of film-makers to face up to the crisis. To not do so, he said, “would be criminal. I think it’s a moral duty. I have children. In different times, I would have made other films. But I make fierce cinema, political cinema, cinema that has no choice.”

Lorius, now 83, said he hoped that among those moved by the movie would be decision-makers attending the Cop21 summit on climate change in Paris this winter. “It’s essential. Governments have met to talk about the problem for years. But we cannot wait to change things. It would be disastrous not to take a decision.” Lorius said he anticipated the film would “touch people more than scientists can”.

Luc Jacquet’s documentary Ice and the Sky Photograph: PR

Although documentary has a rich history of environmental engagement, drama has traditionally been less interested. Yet a groundswell of fiction film-makers have used the festival to expressed an eagerness to tackle the subject.

On Monday, Chariots of Fire producer David Puttnam announced a major new movie about the Arctic 30, the Greenpeace activists imprisoned in 2013 after protesting against Russian oil-drilling in the Arctic. The project, whose collaborators include Emma Thompson, marks Puttnam’s return to film-making after a substantial absence. It was, he said, a reaction to his disillusion with conventional activism and the backlash to the 2005 Climate Change Bill, which he helped oversee. “Rather late in life,” he said, “I’ve had to come to terms with the fact that the only professional tool I have at my disposal is that of a one-time producer.”

Footage also premiered at the festival of Richard Branson-backed drama Chloe & Theo, starring Fifty Shades of Grey’s Dakota Johnson as a homeless woman who befriends an Inuit man who travels to New York after his Arctic hometown is submerged beneath the sea. The film is produced by MTV and, speaking after the screening, their director of social responsibility, said she felt it was within the company’s remit to “bring issues like climate change and other issues that affect young people all over the world to the forefront”.

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Elsewhere at the festival, stars have proved eager to flag the relevance of their films to the debate. Charlize Theron cautioned that the drought and deserts depicted in Mad Max: Fury Road would likely become a reality unless action was taken. “What makes [the film] even scarier is that it is something like that is not far off if we don’t pull it together.”

Even actors whose movies don’t directly engage with the issue appeared to be reading from the same script. Speaking to the Guardian, the actor Gabriel Byrne, whose film Louder than Bombs is freighted with generalised anxiety about the future, said there is “no greater crisis” than global warming. “If we don’t get climate change under control it doesn’t really matter what else we aspire to. We need to make people aware of the real danger of annihilation.”

Byrne compared the current disengagement to Third Reich Germany. “This is everyone’s responsibility. It’s astonishing how sentient adults can either willingly ignore what’s happening or are ignorant of it. Resting nicely in a cocoon of apathy is such a betrayal of the people who come after us, if they come after us.”

As well as using cinema as a consciousness-raising tool, the festival has also attempted to forge new ways to make movie production more eco-friendly. Directors such as Bernardo Bertolucci, Wim Wenders, Walter Salles and Atom Egoyan were among those who endorsed an initiative by Film4Climate to reduce cinema’s impact on the environment.

Said Bertolucci: “There is no doubt the Earth is in danger. I am looking forward to see testimonies about the climate changes.” “It’s time for a global creative and influential alliance to tackle the climate crisis,” added programme manager Lucia Grenna.

For his part, Jacquet agreed that the innovation involved in such action could be a source of new excitement. “If everyone really tackles these issues they will cease to be issues; they will be a source of creativity. If we make a collective effort we will all be stronger after it.”

Lorius echoed the optimism, saying that the spirit of collaboration - between France, Russia and the US, at the height of the cold war - which had enabled first his research served as a model for the future.

Making the movie had raised his spirits, he said. “I was pessimistic but I think that now people are changing. People talk about this almost every day. Everyone knows it’s a problem. A solution is another matter. But man is never so supremely in his element as when facing adversity.”