Obama says the “world has to step up and it has to step up now”.
He says that he doesn’t have all the answers and admits there are times when he feels discouraged and the future seems bleak.
“There are times where I’m doubtful that humanity can get its act together before it is too late,” he says.
But he says “we can’t afford hopelessness” and adds that we’ll have to summon the passion and activism of citizens “to push governments, companies and everyone else to meet this challenge”.
He says that’s what allowed the US to meet climate goals when “even when we didn’t have much leadership on it”.
“It was ordinary Americans making their voices heard,” he says.
Obama goes on to criticise the Republican Party for “sitting on the sidelines” and expressing “active hostility towards climate science,” making it a “partisan issue”.
“That’s got to stop,” he says, adding that saving the planet “isn’t a partisan issue” and climate change can’t be seen “just as an opportunity to score political points”.
To applause from the audience, he says the “most important energy in this movement is coming from young people”.
Obama adds that young people are “right to be frustrated” because his generation has not done enough to tackle climate change.
Barack Obama shares some advice from his mother who told him “don’t sulk, get busy, get to work and change what needs to be changed”.
“Luckily that’s exactly what young people around the world are doing right now,” he says.
He says that two years ago Greta Thunberg inspired people to join the largest climate demonstrations in decades.
“The world is full of Gretas,” he says.
-BBC