Leonardo DiCaprio says he hopes Greta Thunberg's climate change message is a 'wake-up call to world leaders', after meeting with the 16-year-old on Friday.
The award-winning actor, 44, praised the teenage environmentalist, calling her a 'leader of our time' on social media after they spoke in California, US.
He captioned two photographs, one of which showed the pair smiling as they sat outside together, with a paragraph of support for Greta and other climate change campaigners.
Supportive: Leonardo DiCaprio says he hopes Greta Thunberg's climate change message is a 'wake-up call to world leaders', after meeting with the 16-year-old on Friday
Leo passionately penned: 'There are few times in human history where voices are amplified at such pivotal moments and in such transformational ways – but @GretaThunberg has become a leader of our time.
'History will judge us for what we do today to help guarantee that future generations can enjoy the same liveable planet that we have so clearly taken for granted.
'I hope that Greta’s message is a wake-up call to world leaders everywhere that the time for inaction is over.'
Environmentalists: The award-winning actor, 44, praised the teenage environmentalist, calling her a 'leader of our time' on social media after they spoke in California, US
Leo said young activists made him 'optimistic' about the future, before adding it was 'an honour' to meet Greta and make 'a commitment to support one another'.
He added: 'It is because of Greta, and young activists everywhere that I am optimistic about what the future holds.
'It was an honour to spend time with Greta. She and I have made a commitment to support one another, in hopes of securing a brighter future for our planet.' (sic)
He added the following hashtags: '#FridaysforFuture #ClimateStrike @fridaysforfuture.'
In September, Leo laid into President Donald Trump over the environment.
The Oscar-winning actor was speaking in New York at the Global Citizen Festival and criticised the president's 2017 decision to pull out of the Paris climate accords.
DiCaprio said Trump and other world leaders had gambled away the future of the planet by denying climate change.
It's not the first time DiCaprio has spoken out against Trump. In 2017 he chastised him for 'ignoring facts and truths and modern science.'
Making a stand: In September, Leo laid into President Donald Trump over the environment, he was speaking in New York at the Global Citizen Festival and criticised the president's 2017 decision to pull out of the Paris climate accords (pictured ion February 2018)
DiCaprio runs an environmental organisation, Earth Alliance. He recently formed a $5 million fund to protect the Amazon rainforest from increasing fires.
Di Caprio has previously spoken out on climate change during his Oscar acceptance speech in 2016.
He said: 'Climate change is real, it is happening right now. It is the most urgent threat facing our entire species, and we need to work collectively together and stop procrastinating.
'We need to support leaders around the world who do not speak for the big polluters, but who speak for all of humanity, for the indigenous people of the world, for the billions and billions of underprivileged people out there who would be most affected by this.'
Future: DiCaprio said Trump (pictured in August) and other world leaders had gambled away the future of the planet by denying climate change
At the New York conference, DiCaprio also praised Swedish student Greta who spoke at the United Nations earlier this year.
He shamed those who appeared to mock or insult the 16-year-old, including the president.
The TV host described Greta as 'real and raw' during filming for her show in California on Friday.
As Greta walked out on stage to David Bowie's Heroes, the youngster looked overwrought by the studio audience.
Ellen asked the teen climate activist, who suffers from Asperger's syndrome, how she became so passionate about