The 41-year-old "The Revenant" star, who is a United Nations Messenger of Peace, spoke at a landmark gathering held in New York City on Earth Day, and saluted the representatives from 175 countries, who came to the meeting to sign the Paris Agreement on climate change into international law, reported Daily Telegraph.
DiCaprio admitted his recent research into the issue left him "absolutely terrified" about what will happen to the planet if greenhouse gas emissions are not addressed.
"Our planet cannot be saved unless we leave fossil fuels in the ground where they belong.
The longtime environmental advocate also suggested the issue of climate change was similar to that of American slavery, citing historical US leader President Abraham Lincoln, who served during the abolition of slavery and the Civil War.
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"(Lincoln) was speaking before the US Congress to confront the defining issue of his time: slavery," he said.
"Remarkably, his words ring as true today when applied to the defining crisis of our time: climate change."