Assessing ExxonMobil’s global warming projections

Dimitri Lafleur , our Chief Scientist, has summarised the findings of the first scientific review of what Exxon scientists knew and internally published on the causes of climate changes, on the consequences of fossil fuel emissions and estimates of remaining carbon budgets, by G. Supran, S. Rahmstorf, N. Oreskes in Science (2023 ).

ExxonMobil understood as much about climate change as did academics and government scientists.  

The analysis shows that, in private and academic circles since the late 1970s and early 1980s, ExxonMobil scientists:

1. accurately projected and skillfully modelled global warming due to fossil fuel burning
2. correctly dismissed the possibility of a coming ice age
3. accurately predicted when human-caused global warming would first be detected and
4. reasonably estimated how much CO2 would lead to dangerous warming.

Yet, whereas academic and government scientists worked to communicate what they knew to the public, ExxonMobil worked to deny it.

While the Exxon scientists correctly forecasted the impact of the fossil fuel emissions, externally Exxon engaged very differently, exaggerating the uncertainties of climate science and models, and cultivating the myth of a global cooling scientific consensus in the 1990s and 2000s. It contradicts their internal findings that showed that uncertainties were not too great to distinguish human and natural drivers and dismissed the global cooling narrative as early as 1977.

Exxon scientists, often in collaboration with independent scientists, accurately forecasted as early as 1977, the impact of fossil fuel emissions on temperature increase. Internal publications in 1977, 1979, 1980, 1982, 1984, 1985, 1994, 1997, 2001 and 2003 show that their predictions align very closely with the global observational temperature and CO2 concentration records.

Exxon’s assessments of the remaining carbon budget (between 1982 and 2005) to limit global warming to 2C was 251-716 gigatonnes of carbon (GtC) align well with the current 442-651GtC (Rogelj et al, 2016). The academics are not aware of Exxon alerting investors, consumers or the general public about this constraint.

Figure1: Twelve different models. Internally referred to as ‘sophisticated’ and ‘state of the art’, all assessed against current observations (temperature (in red) and CO2 (in blue)). 10 out of the 12 unique projection datasets are consistent with observations.

Figure 2: In 1982, Exxon management were briefed on the CO2 greenhouse effect where this graph was circulated showing ‘an estimate of average global temperature increase’ under the “Exxon 21st century - high growth scenario” for CO2, modelled by Exxon scientists in 1982. The estimate for global temperature increase and atmospheric CO2 concentration is shockingly consistent with the observational record after 1982 (for temperature in red and CO2 in blue). 

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