US oil giant ExxonMobil knowingly misled the public for decades about the danger climate change poses to a warming world and the company's long-term viability, according to a peer-reviewed study.
An analysis of nearly 200 documents spanning decades found that four-fifths of scientific studies and internal memos acknowledged global warming is real and caused by humans.
At the same time a similar proportion of hundreds of paid editorials in major US newspapers over the same period cast deep doubt on these widely accepted facts.
The study also cites ExxonMobil calculations that capping global warming at under two degrees Celsius (3.6 degrees Fahrenheit) -- the goal enshrined in the landmark Paris climate accord -- would impose sharp limits on the amount of fossil fuels that could be burned, and thus potentially affect the firm's growth.
Both findings are relevant to ongoing investigations by state and federal attorneys general, along with the Securities and Exchange Commission, on whether the company deceived investors on how it accounts for climate change risk.
The new study was published in the journal Environmental Research Letters.
Earlier reporting by InsideClimate News, nominated last year for a Pulitzer, unearthed the internal documents and came to much the same conclusion.
In response, the company -- the largest oil producer in the United States, with revenue of $218 billion dollars (185 billion euros) last year -- denied having led a four-decade disinformation campaign.
"We unequivocally reject allegations that ExxonMobil suppressed climate change research," it said at the time. "We understand that climate risks are real."
- Systemic bias -
The company slammed journalists for having allegedly "cherry-picked" data in a way that unfairly put the company in a bad light.
The new study pushes back on that characterisation.
"We looked at the whole cherry tree," Geoffrey Supran, a researcher at Harvard University and co-author of the study, told AFP.
"Using social science methods, we found a gaping, systematic discrepancy between what Exxon said about climate change in private and academic circles, and what is said to the public."
As early as 1979, when climate change barely registered as an issue for the public, Exxon was sounding internal alarms.
"The most widely held theory is that... the increase in atmospheric CO2 is due to fossil fuel combustion," an internal memo from that year read.
A peer-reviewed study by Exxon scientists 17 years later concluded that "the body of evidence... now points towards a discernable human influence on global climate."
At the same time, however, the company was spending tens of millions of dollars to place editorials in The New York Times and other influential newspapers that delivered a very different message.
"Let's face it: The science of climate change is too uncertain to mandate a plan of action that could plunge economies into turmoil," Exxon opined in 1997, as the Bill Clinton administration faced overwhelming opposition in Congress to US ratification of the Kyoto Protocol.
Natasha Lamb, managing partner of investment management firm Arjuna Capital, said the new analysis could bolster the lawsuits accusing ExxonMobil of deliberately downplaying climate change risks.
"The Harvard research shows systemic bias in sowing public doubt, while acknowledging the risks privately," she said after reviewing the study's main findings.
"That is at the heart of the investigations."
- 'Deception and denial' -
Lamb's firm filed the first shareholder proposal in 2013 asking ExxonMobil to assess whether imposing a 2C limit on warming would result in the company not being able to exploit its reserves.
Those efforts were swatted down, but four years later a decisive 62 percent of shareholders called on ExxonMobil, in a non-binding vote last May, to detail how climate change will affect its future.
In three other lawsuits, coastal communities in California are suing 37 oil, gas and coal companies, including ExxonMobil.
Marin and San Mateo counties, along with the city of Imperial Beach, assert that these fossil fuel purveyors knew their product would cause sea level rise and coastal flooding but took no action to inform the public or curtail their carbon emissions.
The new study "confirms some of the central tenets of our cases," said Vic Sher, a senior partner at Sher Edling and a lawyer in the case.
"We will prove that Exxon and the fossil fuel industry knew for decades that greenhouse gas pollution would case warming of the air and oceans, sea level rise, and other consequences," he told AFP.
"The industry engaged in deception and denial while aggressively marketing and making enormous profits."
From 2006 to 2016, ExxonMobil was led by Rex Tillerson, currently Secretary of State under US President Donald Trump.