One of the world's largest oil companies knew it was helping fuel global climate change as early as 1981, according to an email by a former employee. But instead of taking steps to reveal or reduce this risk, Exxon and other oil giants spent decades actively misleading the world about the link between fossil fuels and climate.

This news comes via Leonard S. Bernstein, a climate expert who spent 30 years in the oil industry — including 20 at Exxon and 10 at Mobil before their 1999 merger — and was also a lead author of two major U.N. reports on climate change.

In an emailed response to a question from Ohio University's Institute for Applied and Professional Ethics, Bernstein explains Exxon was aware of the link between carbon dioxide emissions and climate change in 1981, seven years before scientist James Hansen's famous 1988 testimony to Congress. The company was debating whether to make a long-term investment in a carbon-rich gas field, and apparently wanted to anticipate future regulations based on the threat of climate change.

"Exxon first got interested in climate change in 1981 because it was seeking to develop the Natuna gas field off Indonesia," Bernstein writes. "This is an immense reserve of natural gas, but it is 70% CO2." The email was first posted to Ohio University's website in October 2014, but it went largely unnoticed until it was highlighted this week in a new report by the Union of Concerned Scientists (UCS).

"In the 1980s, Exxon needed to understand the potential for concerns about climate change to lead to regulation that would affect Natuna and other potential projects," Bernstein writes. "Natural resource companies — oil, coal, minerals — have to make investments that have lifetimes of 50-100 years. Whatever their public stance, internally they make very careful assessments of the potential for regulation, including the scientific basis for those regulations."

Exxon ended up passing on Natuna, and despite its alleged awareness about how CO2 emissions can affect the atmosphere, it spent an estimated $30 million over the next 27 years sowing doubt about scientific support for such a connection.

Exxon Valdez oil spillCleanup crews skim Prince William Sound after the 1989 Exxon Valdez oil spill. (Photo: Chris Wilkins/AFP/Getty Images)

It's unclear if any other oil companies were thinking about the climate impacts of their projects back in 1981, but as UCS president Ken Kimmell notes in a press release, the industry overall missed its opportunity to lead on the issue.

"Many fossil fuel companies haven't been honest about the harm they have caused by extracting and selling products that place our climate in grave danger," he writes. "Instead of taking responsibility, they have either directly — or indirectly through trade and industry groups — sown doubt about the science of climate change and fought efforts to cut emissions."

In 2008, ExxonMobil pledged to stop funding climate-change denial groups (although there's some evidence the company continued funding climate deniers as recently as 2010). By then, the broad scientific consensus about climate change had become common knowledge, making denial an increasingly unpalatable public position.

ExxonMobil hasn't formally responded to the UCS report, but a spokesman tells the Guardian climate science was hazy in the early '80s. "The science in 1981 on this subject was in the very, very early days and there was considerable division of opinion," says Richard Keil, adding the company now sees climate change as a risk.

Even in light of its track record on climate change, Bernstein describes ExxonMobil as "far more ethical [than] many other large corporations." And based on his experience there, he adds, "I know that much of that ethical behavior comes from a business calculation that it is cheaper in the long run to be ethical than unethical."

Nonetheless, Bernstein's email has led to some speculation about an oil company's liability for knowingly contributing to climate change — and trying to mislead the public about it — for so long. It's reminiscent of tobacco companies' response to their products' public-health risks, according to former U.S. Justice Department lawyer Sharon Eubanks, who led the government's successful 2000-2005 lawsuit against major tobacco companies for obfuscating the dangers of smoking.

"It starts to look like a much longer conspiracy," she tells the Climate Investigations Center. "It's like what we discovered with tobacco — the more you push back the date of knowledge of the harm, the more you delay any remediation, the more people are affected. So your liability can grow exponentially as the timeline gets longer."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.