Arnold Schwarzenegger, Sigourney Weaver, and James Cameron were among the Hollywood celebrities delivering a warning about the dangers of climate change at the Democratic National Convention in Philadelphia on Wednesday.

Schwarzenegger, the Republican former governor of California andsuccessor to Donald Trump as host of Celebrity Apprentice, appeared in a short film produced by Cameron to highlight the immediate and ongoing effects of global warming.

“Because of global warming, mountain snow now melts earlier each year,” Schwarzenegger says in Not Reality TV, over images of raging fires. “When that happens, the ground dries up earlier too.” He is then seen walking through a charred landscape in firefighting gear.