TAPPER: In our Earth Matters Series today, a surprise if brief appearance today from President Trump, who for 14 whole minutes popped in on a climate summit at the United Nations after initially planning to skip it. But climate activists including former vice presidents are calling him out. Let's go to CNN's. Bill, Weir at the U.N. Bill?</s>BILL WEIR, CNN CHIEF CLIMATE CORRESPONDENT: Jake, fittingly, unceasingly warm day here on the east side of Manhattan as world leaders converge to talk about a climate in crisis. The President, as you mentioned, pulling a drive-by less than 15 minutes listening to the prime minister and chancellor of both India and Germany on his way to a meeting about faith protecting religious freedoms around the world. One world leader who knows this topic well, and is back in familiar territory, former Vice President Al Gore.</s>AL GORE, FORMER VICE PRESIDENT, UNITED STATES: Thanks, Bill.</s>WEIR: Great to see you. Thank you for coming outside.</s>GORE: You too always. Thank you.</s>WEIR: What do you make of the lack of American leadership here today?</s>GORE: Well, I think that to focus on the good news side of it, Donald Trump being the face of global climate denial actually is motivating the kind of uprising and enthusiasm we saw last Friday with these millions of young people marching. I'm optimistic. We're behind at the beginning of the second half, but we've got the tools we need to address this crisis.</s>WEIR: It's been over a decade since he tried to sound the alarm at Climate Paul Revere with an inconvenient truth. And after, of course, a lot of fanfare, Nobel Prize for the IPCC scientists behind those initial alarming reports. Very little has been done. The world continues to burn carbon at an unsustainable relentlessly rates. But yet he continues to carry that message with unflappable optimism somehow. Jake?</s>TAPPER: Bill Weir, thanks so much. Our coverage on CNN continues right now.
Trump Makes Brief, Unscheduled Stop At U.N. Climate Summit.