Well before one hottest-year-ever was followed by yet another record-breaker, before Arctic ice vanished in real time and Pope Francis made a plea to save our troubled home, the world’s largest private oil company discovered that its chief product could cause global havoc.

As an accidental public service, this deed was little known until recently, when a trove of documents unearthed by several news organizations showed What Exxon Knew and When It Knew It. And it was reported Thursday that the New York attorney general is starting an investigation to determine whether the company lied about the risks of climate change.

It’s not surprising, given its army of first-rate scientists and engineers, that Exxon was aware as far back as the 1970s that carbon dioxide from oil and gas burning could have dire effects on the earth. Nor is it surprising that Exxon would later try to cast doubt on what its experts knew to be true, to inject informational pollution into the river of knowledge about climate change.

But what is startling is how a deliberate campaign of misinformation — now disavowed by even Exxon Mobil itself — has found its way into the minds of the leading Republican presidential candidates.