I pored over boxes of papers, thousands of pages. I began to recognize typewriter fonts from the 1960s and ‘70s and marveled at the legibility of past penmanship, and got used to squinting when it wasn’t so clear. What those papers revealed is now changing our understanding of how climate change became a crisis. The industry’s own words, as my research found, show companies knew about the risk long before most of the rest of the world.