Filmmaker and noted environmentalist James Cameron produced an extended public-service announcement about climate change that aired during the Democratic National Convention on Wednesday, shortly before a speech by California governor Jerry Brown about the dire effects of global warming. Sigourney Weaver introduced the video and narrated it with contributions from America Ferrera, Jack Black, Don Cheadle, and even Arnold Schwarzenegger. Be warned: It’s exactly as depressing as you think it’s going to be.