This brand new climate change documentary  by Leonardo DiCaprio has been released just before the US goes to the polls to pick a new president (you can watch the whole thing above). While Donald Trump only makes a fleeting appearance, spouting inanities as always, I can’t help but think the timing is far from coincidental.

The name ‘Before The Flood’ is taken from the central panel of a Hieronymus Bosch triptych, The Garden of Earthly Delights, a print of which hung over DiCaprio’s ‘crib’ as a child (not sure I’d pick Bosch to decorate my kids’ rooms but, hey…). In that central panel, the seven deadly sins start to corrupt humankind before the inevitable final panel of doom.

The movie follows DiCaprio as he travels the world talking to local activists, climate scientists and major figures such as Bill Clinton, Barack Obama and the Pope. Here are the key moments that stuck with me:

1. The Mayor of Miami talking our Leo through the $400m the city is spending on flood defences to combat repeated flooding due to sea level rises, then explaining that neither their Governor Rick Scott nor their Senator Marco Rubio believe in climate change. In fact the former is alleged to have banned the term from official communications (although he denies it).
2. In probably the most confrontational piece, Indian activist Sunita Narain had a polite but firm go at Leo for US NGOs telling India and China to skip carbon-intensive development while doing little at home. “What is the US doing that the rest of us can learn from?” she asks pointedly to DiCaprio’s evident discomfort.
3. Lastly, British-born astronaut and climate scientist Piers Sellers who reassured us that if we stop emitting carbon then temperatures will eventually peak and cool back to a reasonable level. “There is hope.” he tells us.

I watch these documentaries like a hawk for errors, and the only tiny blooper I spotted was a graphic with methane as CH⁴ rather than CH₄. But my biggest complaint would be the focus on doom – the ‘solutions’ part consisted of Elon Musk talking about his giga-factory and a montage of renewable energy installations. I felt there was something missing about how low carbon energy is surging, becoming the ‘new normal’ and creating large numbers of jobs. This massive carrot may persuade the hitherto unpersuaded.

Overall, it’s a fine, well put together film, if a tad earnest, about the biggest issue in the world today. The trillion dollar question of course is will it reach out to those who don’t already ‘get it’. Well, Al Gore’s An Inconvenient Truth did back in 2006 and Leo certainly has more sheer star wattage than the notoriously wooden vice-Pres. It may be preaching to the choir, but as an organiser of the Toronto film festival put it, DiCaprio has got “a very large choir.”