It continues to this day. The four companies are members of a powerful pro-coal trade association that in 2014 called climate change a “hypothesis” and argued that carbon dioxide—the air pollutant that causes global warming—was as much as 400 times more beneficial to humanity than it was harmful.

“We can now identify railroads as an integral component of opposition to climate action,” Robert Brulle, an author of the new research and a professor of sociology and environmental science at Drexel University, told me. “There’s no doubt in my mind about that.”

Why did railroads invest millions in climate-science denial? Perhaps because coal makes up almost one of every three tons of American rail freight. Nearly 70 percent of American coal is shipped by rail, often along “dedicated” lines that can “operate around the clock,” the rail association says on its website. The largest class of railroads made a combined $10.7 billion, or 14 percent of their revenue, hauling coal last year. So while rail companies say they emitted only about 0.6 percent of U.S. greenhouse-gas pollution last year, their indirect carbon footprint may be gargantuan.

If you take emissions embedded into coal into account, the railroads facilitated 16.5 percent of total U.S. carbon pollution last year, according to calculations by Rob Jackson, a geoscience professor at Stanford. That’s more carbon pollution than was released last year by all the farms in the United States, or by all the domestic flights, or by all the commercial and residential buildings.

In separate statements, the four railroads said they were committed to sustainability, and noted, correctly, that rail is the most efficient form of ground transportation. CSX said that, as “common carriers,” railroads are required by law to move “all forms of energy.” BNSF and Union Pacific—the two dominant railroads in the American West—explicitly rejected the premise that they had fostered climate denial: BNSF’s statement said it “has never denied the science or existence of climate change,” and Union Pacific said it has not worked to delay climate policy, noting that it has “acknowledged the changing environment and climate risk in public filings since 2007, while reporting fuel consumption and greenhouse gas reduction initiatives in [filings] since 2009.”

But railroads’ efforts to keep coal burning—and all those tons of carbon flowing into the sky—have been hidden in plain sight for decades. Two new studies unearthed their influence this fall.

The first, by Brulle, compiled 25 years of data about companies and nonprofits involved in “the organized efforts to oppose meaningful climate action,” he said. He found that the railroads kept appearing in crucial coalitions that blocked policy and pushed climate-science denial.

His results, published in the journal Sociological Inquiry in October, showed that railroads often waged this fight alongside other coal-dependent companies, including steelmakers, electric utilities, and coal-mining firms themselves. Brulle now argues that this “coal-utilities-rail-steel sector” makes up an important but little known coalition opposed to climate action.