Al Gore travels the country delivering the slideshow presentation on climate change that became the spine of his post-political career, and director Davis Guggenheim intercuts it with Gore's own reflections on his sister's death from lung cancer, his son's near-fatal accident, and the 2000 election loss that redirected his life toward this cause. The presentation itself is dense with graphs and satellite images: shrinking glaciers in Greenland and Kilimanjaro, a Antarctic ice core record stretching back 650,000 years, and projections of Manhattan and Florida under rising seas. Gore walks the stage with a laser pointer and a wry sense of humor, building an argument that carbon dioxide levels track temperature with unsettling precision. The film treats the science as settled and Gore as its most persistent messenger, mixing auditorium footage with home movies and archival clips of a changing planet. It became one of the highest-grossing documentaries ever made and helped push climate change into mainstream political debate, for better or worse depending on which side of that debate you sit.