Ten years since Al Gore presented An Inconvenient Truth, climate change has taken a bit of a back seat. Leonardo DiCaprio on the other hand has famously been keeping watch. For fifteen years, he met figureheads and presented interviews with Presidents on the issue, and Before the Flood serves as an update of all his efforts.

But this is not what we’ve achieved or a celebration of the alternate power sources we’ve turned to. Before the Flood reveals that predications were way off and things have got much worse. Director Fisher Stevens tries to balance this brutal reality check with stories of hope for the future but the truth is we’ve passed the tipping point.

Before the Flood is bookended by DiCaprio’s childhood memories of Hieronymus Bosch. Above “his crib”, his creative parents stuck a poster of the triptych, The Garden of Earthly Delights. The Garden of Eden is on the left, in the centre is a world where sin creeps in and then hell is situated on the right. This provides a structure for the film as he fears we are slipping into that final panel. This leads to DiCaprio explaining his role in the United Nations as “Messenger of Peace” for climate change. This was a role he accepted knowing that he’d receive criticism. Fox Television mocks him, as they would mock climate change. But this position is the impetus for Leo to jet off around the world, personally visiting those affected by climate change.

He witnesses the immediate impact on China, as they wear masks to protect themselves from pollution and invest in solar energy on an enormous scale. He speaks to Sunita Narain, an Indian environmentalist , and she explains how little electricity is used in India, with a comparison to the excessive amount used by Americans. You’ll see a section on beef and it’ll make you decide to eat less beef, but more chicken. Then there are the Pacific islands, and in particular, Kiribati. In 1999, two islands, Tebua Tarawa and Abanuea, disappeared underwater. Luckily, they were uninhabited but it has meant that residents of Kiribati have to put in place a plan for migration. Water levels will rise and the island will be no more. The climate has changed and the consequences are already playing out.

What separates Before the Flood from ground-breaking films such as The Cove and Blackfish, is its Hollywood star at the centre and the broad spectrum of content he’s sharing. DiCaprio knows he is using his star power to create awareness on the issues and, unless you listen to paid-off Republicans, you’ll be acutely aware that climate change is a global problem we aren’t tackling fully. With this in mind, Before the Flood becomes an essential piece of filmmaking. The environment is constantly changing and the power of democracy is what’s needed to change hearts and minds. Before the Flood reminds us of this escalating problem that a mere lightbulb-change won’t solve. Still, in 2016, people are not convinced of the necessity of wind and solar power, despite countries like Norway, Germany and Sweden leading the charge with so much power dependent on renewable energy. Let alone the fact that Norway has so much energy created by renewable sources, it exports the majority of it to neighbouring countries.

Before the Flood can only briefly touch upon the wider issues of social change. Capitalism, corrupt politicians and a culture of inequality all plays a part but, in fairness, this is a bigger problem. Though a 90-minute documentary can’t truly tackle this, it does connect Before the Flood with Michael Moore’s Where to Invade Next and Khushboo Ranka and Vinay Shukla’s An Insignificant Man, as they show social and political change on a national level.

Between conversations with Barack Obama, John Kerry and, somewhat awkwardly, The Pope, DiCaprio’s final moment in the UN, delivering a speech on the issues raised is powerful, profound and urgent. He hasn’t just seen melted glaciers in Greenland and expansive oil fields in Canada; he has seen the consequence on the poor. Their entire livelihood wrecked on one side of the world due to the greed on the other side. Some of the global changes necessary are coming, and astronaut Piers Sellers explains what they’ve been cooking up in NASA that’ll force people to take responsibility. Before the Flood embarks on a major journey, with DiCaprio at the helm of the ship, and forces us to realign where our priorities lie. Essential, informative and deeply worrying, Before the Flood will be a film you’ll be showing children for years to come. Let’s hope it marks a turning point for change.

This served as part of my coverage for the London Film Festival 2016, for Culturefly