Leonardo DiCaprio has met with Greta Thunberg, calling the 16-year-old 'a leader of our time' and revealing the two campaigners have 'made a commitment to support one another'.

The Oscar winning actor - who has been widely criticized for his use of private jets despite his interest in environmental causes - said it was an 'honor' to speak with the climate activist, posting an image of the two of them together on Friday.

In an Instagram post Leo said he hopes Greta's message is 'a wake up call to world leaders', adding that the schoolgirl makes him 'optimistic about what the future holds'.

It comes as Greta took to her own social media pages pleading for help in getting to the United Nations’ COP25 climate change summit.

She had been heading to Chile but after a location change from Santiago to Madrid she has 'traveled half around the world, the wrong way'.

Greta, who refuses to travel by plane for environmental reasons, wrote: 'Now I need to find a way to cross the Atlantic in November... If anyone could help me find transport I would be so grateful.'

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, pictured

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. DiCaprio has been widely criticized for his use of private jets despite his interest in environmental causes

In September DiCaprio, who used his acceptance speech at the 2016 Academy Awards to urge lawmakers to 'stop procrastinating' about the issues surrounding climate change, came out in support of Greta at a New York conference.

But he has been criticized in the past for his use of private jets. In 2014 emails hacked from film studio Sony, it was revealed he took six private flights in just six weeks which cost $177,550. This travel included two round trips from Los Angeles to New York, and one from LA to Las Vegas.

In 2016 he hosted his annual eco fundraiser gala, which saw an impressive cast of A-listers descend on St Tropez to raise funds for various conservation projects before hopping off a helicopter to board a gas guzzling private jet two days later.

To add insult to injury, he was driven by golf buggy across the airport runway for the short distance between the two.

And Leo took a private jet twice in May of that year to pick up an environmental award in New York - before flying back to a glitzy gala in France.

But it didn't stop The Revenant star from laying into President Donald Trump over the environment. Speaking at the Global Citizen Festival DiCaprio also criticized 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 become clear that our political leaders have failed to live up to promises that we celebrated that day,' DiCaprio said.

'Our future is being gambled away, and our leaders, those whom we entrust to protect us and set the example, are either failing to stop these dangerous trends or, in some cases, denying the very science of this climate catastrophe,' he added.

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.'

'Unless you live in an alternate reality, there's no more time for denial,' DiCaprio said. 'A carbon-neutral future is the only way we will inherit a planet capable of sustaining life on Earth as we know it.'

In September, Leo laid into President Donald Trump over the environment, he was speaking in New York at the Global Citizen Festival, pictured, and criticized the president's 2017 decision to pull out of the Paris climate accords

Leonardo DiCaprio speaks onstage during the 2019 Global Citizen Festival: Power The Movement in Central Park on September 28

DiCaprio said Trump (pictured in August) and other world leaders had gambled away the future of the planet by denying climate change

DiCaprio runs an environmental organization, Earth Alliance. He recently formed a $5 million fund to protect the Amazon rainforest from increasing fires.

In his Oscar acceptance speech 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.'

Leo's Instagram update came just hours after Greta said speaking directly to Trump would be 'a waste of time' while on the Ellen DeGeneres show.

The TV host described Greta as 'real and raw' during filming for her show in California on Friday.

Ellen DeGeneres asked the teenage environmental activist if she would meet with Trump

'Real and raw': Talk show host Ellen praised Greta when she appeared on her show

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 environmental causes.

She also asked Greta about President Trump's tweet that mocked her speech to the UN in September and wondered whether the teenager would 'sit down' with him to 'explain' climate change.

But Greta replied: 'I don't understand why I would do that. I don't see what I could tell him that he hasn't already heard. And I just think it would be a waste of time, really.'

The host went on to pay tribute to the Swedish schoolgirl, who inspired millions around the world to join her on strike against inaction on climate change.

Ellen asked Greta how she became so passionate about climate activism after learning about it at school.

She replied: 'I just couldn't really believe it, because if this was really true then surely someone must have done something, then surely we would take it seriously.

'But no one took it seriously, so I started to read about it and of course the more I read about it and the more I understood and once I fully understood I couldn't just look away anymore.'

Ellen revealed they had been trying to get Greta on the show for two months but had to wait while she traveled by yacht for two weeks across the ocean to New York and then caught a train to Burbank, California, where the program is filmed.

Greta shared this picture of herself with her trademark placard last night - saying she did not need to dress up for Halloween to scare her critics

the Swedish activist said she did not celebrate Halloween in Sweden but would 'give it a try' in order to troll her detractors

The climate crusader also mocked her detractors on Thursday by dressing as herself for Halloween - saying she terrifies her critics.

The teenage activist said she scared 'a bunch of angry climate crisis deniers' without having to dress up.

Posing in a black-and-white photo with her trademark 'school strike for climate' placard, she said she did not celebrate Halloween in Sweden but 'thought I might give it a try' to troll her critics.

She is currently touring North America and has drawn large crowds at environmental rallies.

'So today is Halloween. I don’t celebrate it back home, but I thought I might give it a try,' she wrote on Twitter.

'And apparently when it comes to scaring a bunch of angry climate crisis deniers - I don’t even have to dress up!'

Greta's activism has prompted an angry response in some quarters and the teenager drew the ire of Donald Trump at a UN summit in September.

At the UN she tore into world leaders in a memorable speech, accusing them of 'stealing my dreams and my childhood with your empty words'.

Trump, a climate change skeptic, tweeted she 'seems like a very happy young girl looking forward to a bright and wonderful future'.

Greta later adopted the description for her own Twitter profile.

Her angry glare at Trump after he upstaged her by walking into the climate summit with his entourage also became a viral sensation.

After her appearance in New York she said online trolls had taken aim at her 'looks, clothes, behavior and differences'.

Greta, center, at a climate protest in Vancouver last week. The teenager's demonstrations have grown from a solo protest to a worldwide movement

Greta can be seen, center, marching during a climate rally in Vancouver last week

Earlier this week Greta turned down a £40,000 environmental prize, saying her movement 'does not need any more awards' but instead needed politicians to listen.

Her campaign began in August 2018 when she started skipping school once a week to stage solo protests outside Sweden's parliament.

The protests quickly drew support and thousands of people have turned out at three climate rallies she has attended in North America.