NBCUniversal Inc. November 20, 2019 3:11 am ‘Late Night': Al Gore Calls Climate Change Most Serious Challenge Al Gore calls climate change the most serious challenge human civilization has ever faced and talks about an upcoming global event for climate change awareness. US & World Videos 2:43 ‘On the Dot' to redevelop stretch of Dorchester Avenue 1:49 Finalists in math competition hope their model helps ease housing crisis 14:31 @Issue extra: Seth Moulton on pro-Palestinian protests, TikTok and more 2:31 Celtics preparing for pivotal Game 3 against Heat in Miami 1:17 Patriots player visits Franciscan Children's Hospital