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Exxon knew just how much fossil fuels could warm the planet as early as the 1970s, study says

Climate activists protest on the first day of the ExxonMobil trial outside the New York State Supreme Court building on October 22, 2019 in New York City.AFP via Getty Images

Scientists at Exxon predicted future global warming with stunning accuracy as early as the 1970s, even as the firm has publicly contradicted its own findings and sowed doubt about climate change, according to a new analysis that puts a number on exactly how much the oil and gas giant knew.

The report from Harvard University and the Potsdam Institute for Climate Impact Research, published in the journal Science on Thursday, marks the first quantitative review of Exxon’s climate science from the past four and a half decades. The findings show that Exxon did not merely have a vague idea that using its products would heat the planet; rather, it had the very specific knowledge that fossil fuel burning would lead to about 0.20 degrees Celsius of global warming per decade, plus or minus 0.04 degrees.


“The precision and accuracy help to cement the argument that ‘Exxon knew’ by making clear what they knew,” said Naomi Oreskes, a Harvard history of science professor who coauthored the report.

Long before climate change became a public issue, Exxon not only knew about the threat of global warming, but also employed teams of researchers to probe that threat, even launching its own ambitious program to build rigorous climate models, investigative journalists found eight years ago. The reporting sparked a rallying cry — “Exxon knew” — and kicked off protest movements, Congressional hearings, and more than a dozen lawsuits.

One of those lawsuits was waged in 2019 by current Massachusetts Governor Maura Healey, then the state’s attorney general, in a bitter saga that saw Exxon slinging allegations of political motives. After a three-year probe into the company’s actions, Healey alleged Exxon knew its products were contributing to dangerous changes in the climate yet hid that information. In May 2022, Massachusetts’ Supreme Court rejected ExxonMobil’s bid to dismiss that lawsuit, which is ongoing today. Two months before that, the company also lost a bid to revive a lawsuit claiming that both Massachusetts and New York’s attorneys general had political motivations for opening such investigations into the company.


The new study could have massive practical implications for ongoing attempts to hold Exxon accountable for its history of climate deception, said the paper’s lead author Geoffrey Supran, associate professor of Environmental Science and Policy at the University of Miami’s Rosenstiel School of Marine, Atmospheric, and Earth Science.

“It strengthens the case that they misled the public,” he said. “We found Exxon’s scientists at no point entertained the possibility that human-caused warming wouldn’t occur because of fossil fuels ... yet they continued to sell them, to promote doubt.”

Exxon spokesman Todd Spitler said in response to the study on Thursday that “those who talk about how ‘Exxon Knew’ are wrong in their conclusions.”

He pointed to a related 2019 case ExxonMobil won in New York, highlighting a section in which Justice Barry Ostrager of the New York State Supreme Court wrote: “What the evidence at trial revealed is that ExxonMobil executives and employees were uniformly committed to rigorously discharging their duties in the most comprehensive and meticulous manner possible. ...The testimony of these witnesses demonstrated that ExxonMobil has a culture of disciplined analysis, planning, accounting, and reporting.”

Researchers in the new study analyzed climate predictions from more than a hundred internal company documents, as well as peer-reviewed scientific publications from Exxon scientists, from 1977 to 2014. The documents came from public archives provided by ExxonMobil Corp., InsideClimate News, and Climate Investigations Center.


To get a sense of the accuracy of Exxon’s research, the authors first compared charts pulled from the company’s documents with data on historical observations, finding remarkable similarities. For instance, a 1982 Exxon study showing growth in CO2 emissions and increases in global temperature over time, based on an assumption that fossil fuel usage would grow closely matched temperature changes that were actually observed in later years.

A chart from a 1982 Exxon study showing both growth in CO2 emissions and increases in global temperature over time, is overlaid with observed CO2 concentrations and observed temperature changes.Science/Science (Science #379), ExxonMobil

In fact, Exxon’s global warming projections were as accurate as those from independent climate scientists and the federal government, and its climate models were so uncannily precise they rivaled projections developed by esteemed NASA scientist James Hansen.

“That shows Exxon’s climate modeling was at least comparable in performance to that of some of the most influential and respected independent climate modelers, ever,” said Supran.

Despite the extreme sophistication of this climate research, Exxon consistently contradicted these findings in public, the report says.

“ExxonMobil spokesmen, including its CEOs Lee Raymond and Rex Tillerson, spent decades denigrating climate models, claiming or suggesting that their uncertainties were so great as to make it impossible to use them in decision-making,” said Oreskes. “Our new study shows their own scientists’ work showed this wasn’t true ... None of their models suggested that climate change would not occur.”

In one example, the authors cite a 2001 press release from ExxonMobil Corp., which asserts that “there is no consensus about long-term climate trends and what causes them,” and goes on to say that “during the 1970′s [sic], people were concerned about global cooling.”


Some scientists in the 1970s did discuss the possibility that a new Ice Age was on the way because of changes in Earth’s orbit known as Milankovitch cycles, said Oreskes. But Exxon’s researchers predicted back in the 1970s that the impact of human-caused greenhouse gas pollution would “swamp the Milankovitch cycle effect and lead to global warming,” she said, as illustrated by a 1977 Exxon projection for average global temperatures, which mirrored real temperature data.

A 1977 Exxon projection for average global temperatures, which the authors overlaid with real temperature data.Science #379/Science (Science #379), Exxon

Brown University sociologist Bob Brulle, who has researched how fossil fuel companies spread climate denial, said this study illustrates Exxon’s long history of “climate deception.”

“This removes any last vestiges of doubt that Exxon didn’t understand what was involved in climate change,” he said.

Dharna Noor can be reached at dharna.noor@globe.com. Follow her on Twitter @dharnanoor.