Leonardo DiCaprio and Secretary of State, John Kerry spent time together discussing solutions for global warming at a climate summit in Paris. DiCaprio, who has been appointed U.N. Messenger of Peace for the Climate, and Kerry, who fought for environmental reform during his time in the Senate, joined hundreds of world leaders in the public and private sector gathered for the Paris Climate Conference, held from Nov. 30 to Dec. 11.

According to People, the Secretary of State tweeted a picture of the meeting, captioning, "Great to see my friend @LeoDiCaprio at #COP21 -- one of the most committed advocates for our ocean and our planet." DiCaprio wrote back Tuesday morning, saying, "Great seeing you, too. Thank you @JohnKerry for all you're doing at #COP21." 

DiCaprio spoke in front of mayors from major cities around the world on Friday at City Hall in Paris to discuss how they can help avert environmental disaster. "Climate change is the most fundamental and existential threat to our species. The consequences are unthinkable and worse, it has the potential to make our planet unlivable," he said, according to The New York Times. 

Daily Mail reports that speaking at a climate summit for city leaders in Paris, DiCaprio said rising temperatures posed the 'most fundamental and existential threat' to human beings, warning ' the consequences are unthinkable, and worse it has the potential to make our planet unlivable.

Speaking in the grand setting of Paris's Hotel de Ville, DiCaprio said the world needed to move away from fossil fuels, and hailed cities such as Vancouver which has pledged to switch to 100 per cent renewable.

He described the UN talks that are taking place in the French capital as 'what may be the most important conference of everybody's lifetime', one that had been 20 years in the making, and said that at previous meetings in Kyoto and in Copenhagen six years ago, countries had come up short. 'This time must be different because we are fundamentally running out of time,' he urged.

He welcomed moves by 392 cities, home to more than 361 million people to sign up to taking action against climate change under the 'compact of mayors' and challenged the mayors, city and regional leaders to do more.

He told them whatever agreement was reached in the UN talks; they were the 'catalysts' for the real work that lay ahead. And he said: 'We are now in a race to better ourselves, to better the planet.

Our future will more prosperous when we are free from the grip of fossil fuels. Now to get there, we must act. We must finally leave behind the inefficient technologies of another century and the business models that they have created.