Currently, the major oil companies appear to have settled on an awkward compromise with the reality of climate change: They generally acknowledge that their product is helping drive it but plan to continue to produce as much of that product as they can. But that reflects a major change for these companies, which up until recently were funding think tanks that minimized the risks of climate change and, in many cases, directly denying the validity of the science.

In the case of ExxonMobil, that includes denying its own science. Thanks to documents obtained by the press, we now know that Exxon sponsored its own climate researchers who did internal research, collaborated with academic scientists, and came to roughly the same conclusions about carbon dioxide that the rest of the scientific community had—and executives were made aware of it.

But how rough were the conclusions that Exxon's scientists gave its executives? It's a question that goes to the heart of how misleading the executives were being when they downplayed the risks. A new study answers that question pretty definitively: Exxon's scientists were as good (and sometimes better) than the scientific community as a whole at projecting the climate changes created by fossil fuel use.

A legacy in graphs

Exxon's scientific climate work was shut down a long time ago. But the new paper relies on the work of two science historians (Geoffrey Supran and Naomi Oreskes), who dug through old documents and a number of peer-reviewed papers to identify cases where Exxon's scientists made projections about how carbon dioxide emissions might alter the future climate. In several cases, we know that the graphs that they found were part of documents that were sent to Exxon executives.

The historians collaborated with a noted climate scientist (Stefan Rahmstorf), who then compared their projections to the behavior of the actual climate. This allowed the team to determine whether the projections made internally at Exxon were in line with those produced by academic climate scientists and whether they were "skillful," meaning that they were in line with what the actual climate ended up doing.

Overall the historians came up with 16 different climate projections produced by Exxon scientists between 1977 and 2003. For most of this era, computer power wasn't sufficient to run the sort of complete-atmosphere climate models that are used today. Instead, the models they used were generally physics-based energy distribution models that tracked things like where and how much radiation gets absorbed, and how air circulation moves that energy around.

Nevertheless, the projections of future warming done by Exxon scientists were remarkably good. Most of them (nearly two-thirds) had error bars that overlapped with the errors in the temperature record. And a couple of the exceptions were simply due to graphs that lacked error bars, narrowing down the potential to overlap with anything considerably. Two of the remaining ones also forecast more warming than actually occurred.

A climate projection's skillfulness is a measure of how closely it agreed with the historic record. And again, Exxon scientists performed well. The aggregate skillfulness of their internal climate models is over 70 percent. By that measure, they outperformed contemporary models from the scientific community.

Internal contradictions

The paper notes other aspects of Exxon's research that were incompatible with statements made by company executives. None of the internal research was consistent with global warming not occurring; all of their modeling indicated that at least some warming was inevitable. The Exxon researchers also concluded that the human influence on the climate should be detectable in the year 2000, give or take five years. The 1995 IPCC report was the first to indicate that a signal of human warming was clear.

Finally, the Exxon scientists estimated a carbon budget to keep future temperatures below 2° C. While its error bars are larger than more recent estimates, they definitely overlap.

Again, some of this information was being given to executives even as Exxon executives were making statements suggesting that climate change might not be much of an issue and funding groups that went much further in dismissing it. We knew this was a problem since Exxon's internal documents initially leaked. What this new study makes clear is that Exxon's scientists were telling everyone almost exactly what the rest of the scientific community was. And that their predictions were, unfortunately, extremely accurate.

Science, 2023. DOI: 10.1126/science.abk0063  (About DOIs).