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Documenting Climate Change Deception

1.12.23

ExxonMobil scientists' projections of global warming were at least as good as those of government and academic scientists in the period from 1977 to 2003.

Photomontage illustration by Niko Yaitanes/Harvard Magazine; photographs by Unsplash


ExxonMobil scientists' projections of global warming were at least as good as those of government and academic scientists in the period from 1977 to 2003.

Photomontage illustration by Niko Yaitanes/Harvard Magazine; photographs by Unsplash

Between 1977 and 2003, ExxonMobil scientists, and the executives to whom they reported, not only knew that climate change was real, they produced some of the best projections and models of global warming that existed at the time, even as their public communications strategy was to promote doubt about the truth. So claims a Science study published January 12, 2023, which finds that even as fossil fuel interests denied that climate change existed or was caused by human activity, scientists in the industry’s employ were forecasting rising temperatures with great skill and accuracy.

The study, coauthored by research associate in the history of science Geoffrey Supran, a 2017 recipient of a Harvard Climate Change Solutions Fund grant, together with Lea professor of the history of science Naomi Oreskes, examined 12 documents, including seven memos internal to ExxonMobil that were produced between 1977 and 1985, and five peer-reviewed papers published between 1985 and 2003. These contain “16 distinct temperature projections,” some of which were models run or built by ExxonMobil scientists, write the coauthors, who rated the projections by assigning them a skill level based on how closely they matched subsequently observed temperatures (through 2019 or the latest projected year, if earlier). They found that the projections were “consistent with, and at least as skillful as, those of independent academic and government models.” In fact, the ExxonMobil projections were better than those provided in testimony to Congress by NASA scientist James Hansen. “The highest-scoring projection was a 1985 peer-reviewed publication produced by ExxonMobil” which earned a score of 99 percent. An earlier 1982/1984 projection garnered a score of 82 percent, and only three of the 16 projections received scores below 50 percent. “For comparison,” the authors write, “NASA scientist James Hansen’s global warming predictions presented to the U.S. Congress in 1988 have been found to have skill scores ranging from 38 to 66 percent across three different [high-, middle-, and low-emissions] forcing scenarios that he reported.”

The study also reports that ExxonMobil accurately predicted when human-caused global warming would first become “discernible against the backdrop of natural climate fluctuations. Ten internal reports and one peer-reviewed publication spanning 1979–1985 offered quantitative estimates,” the research found, “with a median year of 2000 ± 5.”

One set of temperature projections reveals that the company understood that the oceans would absorb much of the heat trapped by greenhouse gases, damping the effect on global average air temperature. Another projection included a model for “sea level response.” And the company “reasonably estimated” how much CO2 could be added to the atmosphere while holding human-caused global warming below 2°C. Their estimates—251 to 716 gigatonnes of carbon (GtC) between 2015 and 2100—are consistent, Oreskes and Supran write, with “recent calculations [that] have narrowed the uncertainty and place the figure at 442 to 651 GtC. Yet, to our knowledge,” they point out, “ExxonMobil did not alert investors, consumers, or the general public to this constraint.”

Instead, the paper states, “Exxon’s public affairs strategy was—as a 1988 internal memo put it—to ‘emphasize the uncertainty in scientific conclusions regarding the potential enhanced greenhouse effect.’” For instance, ExxonMobil Corp CEO Raymond Lee wrote in 2000 that “[W]e do not now have a sufficient scientific understanding of climate change to make reasonable predictions and/or justify drastic measures...the science of climate change is uncertain....” And in 2013, then-CEO Rex Tillerson said: “[T]he facts remain there are uncertainties around the climate...what the principal drivers of climate change are...[T]here are other elements of the climate system that may obviate this one single variable [of burning fossil fuels]...And so that’s that uncertainty issue...”

Exxon scientists, however, “did not particularly emphasize uncertainty,” assert Supran and Oreskes. Instead, their projections included uncertainty levels similar to those reported by academics. And at least two of the company’s scientists warned their superiors of a “carbon dioxide-induced ‘super-interglacial,’” that would “render Earth hotter than at any time in at least 150,000 years.”

As local and state governments sue oil and gas companies for their efforts to deceive the public about the dangers of climate change, the paper provides a troubling assessment of what one company knew, and when.

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