FRONTLINE opens its three-part investigation into the fossil fuel industry's response to climate science with the story of what oil companies knew and when. Interviews and internal documents trace how Exxon's own scientists modeled global warming with striking accuracy as far back as the late 1970s, warning executives that burning fossil fuels would raise global temperatures within decades. Rather than act on those findings, the film shows how the industry funded think tanks, lobbyists, and skeptical scientists to manufacture public doubt, borrowing tactics from the tobacco industry's earlier campaign against smoking-cancer research. Archival news footage, congressional hearings, and former industry insiders lay out the strategy in detail, from early PR memos to decades of testimony downplaying the certainty of climate science. The episode builds a documentary paper trail rather than a polemic, letting internal corporate records carry much of the argument. It sets up the series' larger question: how a handful of companies shaped decades of public and political response to a crisis they understood earliest.