Star Leonardo DiCaprio has a message for the world: that climate change is a very real threat to millions of people around the world, and governments and the public should act now to avoid the worst impacts.

DiCaprio, a United Nations Messenger of Peace, told that organization: "A massive change is required right now. One that leads to a new collective consciousness. A new collective evolution of the human race, inspired and enabled by a sense of urgency from all of you."

DiCaprio was speaking after world leaders came together to agree to limit global warming to 2°C, after meeting in Paris last winter. The actor's words appear in the upcoming documentary film Before the Flood, which will air on National Geographic channels October 30.

The film features DiCaprio as he travels around the world meeting those most affected by climate change and exploring solutions, from renewable energy to protecting against rising seas.

On Monday, DiCaprio is taking his film to the White House, where it will be shown in a special screening for the country's leaders. He will also speak with President Barack Obama about ongoing efforts to address climate change. Leading climate scientist Katharine Hayhoe will also share a sense of what's at stake.

This unique panel discussion will be streamed live and will be available for viewing on the National Geographic Facebook page, starting at 7 p.m. ET tonight. Click here to watch.