Former US vice-president Al Gore has been in Australia to launch An Inconvenient Sequel. Credit:Ben Rushton "I learned at an earlier time in my life, when I almost lost a child, that there are people who carry unbelievably heavy burdens," Gore says. "So I compare what I went through to what millions of people are going through every day. "How can I possibly do anything other than pick myself up and go forward? And I'm very grateful – genuinely grateful – to have found a way to make a difference outside the political world." When an An Inconvenient Truth became a hit in 2006, Gore made a real difference to the debate about climate change. Directed by Davis Guggenheim and based on Gore's travelling slide show about global warming, the documentary took a largely niche discussion for scientists, policymakers and environmentalists into the mainstream.

Co-directors Bonni Cohen, left, and Jon Shenk with Al Gore at a screening of the latest movie in New York. Credit:Evan Agostini As well as winning two Oscars, it took $US50 million at the worldwide box office – impressive for a political documentary – and Gore shared the Nobel Peace Prize in 2007. "It was such a monumentally successful documentary," Jon Shenk, who co-directed the sequel, says. "Pretty much using any metric – not the least of which was fabulous box office returns – the film really gave so many people in the world the vocabulary to talk about the climate crisis and understand the risk to the global climatic system." Despite a seismic shift away from fossil fuels to renewable energy since An Inconvenient Truth, the sequel shows that climate change remains a polarising issue. It follows Gore as he campaigns around the world, training what he calls climate leaders, and negotiating behind the scenes at the Paris climate summit in 2015.

Gore says he was reluctant, for reasons of vanity, to risk being in another documentary. "To tell you the truth, I know so little about movies that I was reluctant to make the first movie but they talked me into it and I'm so glad that wiser heads prevailed," he says. "When I met the directors of this movie, Bonni Cohen and Jon Shenk, they made me realise they had the skill and talent to do something new and different and to further the message and there's so much more work that needs to be done." Despite countless setbacks, including President Trump withdrawing the US from the Paris climate accord this year, An Inconvenient Sequel reflects Gore's relentless optimism about global warming. "When President Trump made his announcement that he wanted to withdraw the US from Paris, I worried that other countries would follow his lead," he says. "But, quite to the contrary, the rest of the world has redoubled its commitment.

"And in the US, state governments and city governments and businesses have said 'We are going to meet the goals anyway'. "The latest trend in the numbers shows that the US is likely to meet or exceed the commitments made by former President Obama regardless of what Trump does." Gore has had numerous meetings with President Trump but revealed his frustration about the results at a Q&A session that followed a screening of An Inconvenient Sequel for supporters in Sydney. "Winston Churchill [once] said the American people generally do the right thing after first trying every available alternative. We're trying one of the available alternatives and it's not working very well. I've had it with Donald Trump. My God!" But Gore believes the battle is being won – "the train is leaving the station" – despite the political showmanship.

"We're going to win this," he says. "There have been two dramatic changes in the last decade. "Number one is the startling decline in the cost of electricity from renewable sources and it continues to go down. "The second big change is the incredible rise in the number of climate-related extreme weather events and they're becoming more and more destructive. Even people who don't necessarily use the phrase global warming in everyday conversation are noticing that Mother Nature is speaking up now." Before making the new documentary, Shenk says Gore gave the filmmakers a 10-hour version of his updated slideshow. "He never really stopped updating that and he continues to work every day to find the latest evidence both about the climate and also about the solutions that now exist," he says.

"Another thing we learned that day was his energy is just so palpable. Bonnie and I call him the Energiser Bunny. He seems to tap into the need to move the needle on this crisis." An Inconvenient Sequel: Truth To Power is in cinemas from Thursday, August 10. Movies that tried to change the world While passionate documentary makers are always trying to change the world, precious few manage it. Michael Moore's inflammatory Fahrenheit 9/11 had as much success stopping George W. Bush being re-elected president in 2004 – absolutely none – as his earlier documentary Bowling For Columbine had in changing US gun laws.

But in 2004, Morgan Spurlock drew so much unflattering attention to McDonald's portion sizes in Supersize Me that the fast-food chain quickly stopped supersizing and has since shifted towards healthier menu options. Joe Berlinger and Bruce Sinofsky's Paradise Lost trilogy, made from 1996 to 2011, led to the release of three Texan men who had been wrongly imprisoned for murder for nearly two decades. Errol Morris' 1998 documentary The Thin Blue Line also led to a wrongly jailed man being released. Three years after Gabriela Cowperthwaite drew attention to the plight of killer whales in captivity in 2013's Blackfish, SeaWorld announced it would stop breeding orcas and the remaining ones would stop performing in theatrical shows by 2019. And just last year, two-time Oscar winner Sharmeen Obaid-Chinoy's A Girl In The River: The Price Of Forgiveness, about a Pakistani teenage girl who survived an honour killing by her father and uncle, prompted then Prime Minister Nawaz Sharif to declare he would change the laws.