Back in 1991, when climate policy was in its infancy, an Exxon subsidiary came to a startling and prescient conclusion about how to curb carbon-dioxide emissions that cause global warming. It would require a heavy price on CO2 pollution before the companies creating emissions would change, the researchers concluded, at a level far higher than almost any in use today.

Calgary-based Imperial Oil Ltd., which has ties to Exxon’s predecessors going back to the end of the 19th century, hired an outside research firm to look at how environmental taxes might affect both CO2 pollution and the Canadian economy. Cutting emissions would only be possible with a price per ton of about C$55, or roughly C$95 ($72) in today’s money and, the researchers argued, the…