Leonardo DiCaprio has been appointed Messenger of Peace of the United Nations.
The Hollywood star will use his new position to try to raise awareness about climate change at a summit next Tuesday (September 23).
He commented: "I feel a moral obligation to speak out at this key moment in human history - it is a moment for action.
"How we respond to the climate crisis in the coming years will likely determine the fate of humanity and our planet."
UN Secretary-General Ban Ki-moon said: "Leonardo DiCaprio is not just one of the world's leading actors. He has also a long-standing commitment to environmental causes, including through his foundation."
