Capping a day-long futurist fair and alternative music fest on the South Lawn of the White House, US President Barack Obama told actor Leonardo DiCaprio and atmospheric scientist Katharine Hayhoe "we're really in a race against time" to curb the worst impacts of climate change.

The hour-long panel discussion followed the premiere of Before the Flood, a documentary on climate change which DiCaprio starred in and produced for National Geographic.

As he introduced Obama and Hayhoe, who directs Texas Tech University's climate science centre, the Oscar-winner said he and director Fisher Stevens wanted their film "to be released before this upcoming election because after first-hand experiencing the devastating impacts of climate change worldwide, we like many of you here today realise that urgent action must be taken".

DiCaprio said: "We must empower leaders who not only believe in climate change but are willing to do something about it. The scientific consensus is in, and the argument is now over. If you do not believe in climate change you do not believe in facts, or in science, or empirical truths, and therefore in my humble opinion should not be allowed to hold public office."


While Obama endorsed the idea of "turning up the dial" to enact even more aggressive carbon cuts globally, he cautioned that incremental steps were essential to making meaningful progress. Recalling that he often instructed his international climate negotiators, "Better is good," Obama said he understood some activists' frustration. "But if we get enough better . . . then that's ultimately how we end up solving this problem."