Leonardo DiCaprio just said something that made millions of people stand up and cheer.

There’s been plenty of star power at the United Nations headquarters this week.

First with Emma Watson’s speech for gender equality and now Leonardo DiCaprio has stepped up to the plate.

In a powerful three-minute speech at the United Nations Climate Change Summit on Tuesday, Leo called for significant international action on climate change.

Warning the world’s leaders: “you can make history or be vilified by it”.

“I stand before you not as an expert but as a concerned citizen,” DiCaprio, a UN Messenger of Peace, told the summit.

“As an actor, I pretend for a living. I play fictitious characters often solving fictitious problems.”

“I believe mankind has looked at climate change in that same way – as if it were fiction.”

The 39-year-old actor and longtime climate change activist has called for the support of renewable energy, setting a price on carbon emissions and eliminating government subsidies for oil, coal and gas.

The climate change summit, currently being held in New York City, is the largest leaders’ climate meeting since the 2009 Copenhagen summit, which failed to reach an agreement on addressing climate change.

Before speaking at the summit, Leo marched with 400,000 others on the streets of New York, one of the hundreds of rallies around the world that drew thousands to the street calling for action on climate change.

“This is the most urgent of times, and the most urgent of messages,” he said.

“Honoured delegates, leaders of the world, I pretend for a living. But you do not. The people made their voices heard on Sunday around the world and the momentum will not stop. And now it’s YOUR turn, the time to answer the greatest challenge of our existence on this planet … is now.”

“I beg you to face it with courage. And honesty.”

Leo even set up an Instagram account for the event.

What do you think of celebrities using their star power to raise awareness of issues, harmful or helpful?