A few years ago, I was sitting in the book-lined study of an elegant condo with a view of downtown Washington, interviewing a former senior Koch Industries lobbyist about his job. I asked him what got him up in the morning when he worked for Koch. He gave me a one-word answer: “Carbon.”

At the time, I had been reporting for years on Koch Industries, one of the largest and most confusingly complex private companies in the world. Its annual revenue is larger than that of Facebook, Goldman Sachs and U.S. Steel combined, and it makes everything from gasoline to nitrogen fertilizer to nylon, paper towels and windows. For all this complexity, one business inside Koch Industries remains more important than the rest — processing and selling fossil fuels.

David Koch, who died Friday at the age of 79, is best known as a major funder of right-wing political causes, from tax cuts to deregulation, an enthusiastic patron of the arts and a man-about-town. But to his critics, his most lasting political legacy might very well be the rapidly warming world that he has left behind.

Koch Industries realized early on that it would be a financial disaster for the firm if the American government regulated carbon emissions or made companies pay a price for releasing carbon into the atmosphere. The effects of such a policy would be measured over decades for Koch. The company has billions of dollars sunk into the complex and expensive infrastructure of crude-oil processing. If a limit on greenhouse gas emissions were imposed, it could dampen demand for oil and diminish the value of those assets and their future sales. The total dollar losses would likely be measured in trillions over a period of 30 years or more.