From 1979 to 1982, research scientists at Exxon studied the impact of CO2 emissions on global climate. The report become public in 2015 as a result of litigation. To me, the most interesting part of the report is the accuracy of the Exxon forecast in predicting the rise of atmospheric CO2 and global temperature.
Berkeley Earth just released their monthly climate report for September, 2025. September 2025 was the third-warmest September on record, behind the two previous years, but well ahead of the decade before that. The 12-month global rolling average was also slightly cooler than 2023 and 2024, but noticeably warmer than the previous decade, and still on trend with accelerating warming since about 1970.
I overlaid the image of the Berkeley Earth chart and my own chart of average global CO2 (drawn from the Scripps Institute CO2 observatory network) on the Exxon chart. The Exxon scientists did a remarkable job in forecasting, considering that the forecast was made 45 years ago. The Exxon researchers' forecast was about 10% high on the increase in CO2 concentration, and about 15% high on the increase in global temperature.
Exxon scientists forecast that atmospheric CO2 would rise from 338 parts per million (ppm) in 1980 to about 435 ppm in 2025, compared to actual CO2 of about 426 ppm in 2025 The scientists forecast an increase in global temperatures of 1.15 degrees Celsius, compared to 2025 observations of about 1.0 degrees above the global temperature in 1980.
The Exxon report said we would not be able to unambiguously detect global warming before 1995 at the earliest, to get beyond the range of normal temperature fluctuations. They said it was possible that CO2 induced warming might not be clearly detected until 2020. The report concluded that warming was not likely to cause substantial climatic changes until the average global temperature rose at least 1 degree C above 1980 temperatures, but that is exactly the global temperature we see today. The scientists also reported that there was concern that once climatic impacts are measurable, they might not be reversible.
The report stated bluntly that “Mitigation of the ‘greenhouse effect’ would require major reductions in fossil fuel combustion.” There was some discussion of possible fuel switching to fuels with lower carbon emissions, and the potential economic impacts of those changes.
So, the Exxon guys called it nearly 50 years ago.
We’re 45 years farther along, but we have changed little in our forecasts or outlook. There is little doubt that atmospheric CO2 levels will continue to rise for some decades, and that the world will continue to get warmer. Consequences of that warming are now the meaningful topic.
Exxon global CO2 and temperature forecast, 1982 internal report, with overlay of observed global average temperature reported by Berkeley Earth.
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C.D. Keeling et al, Scripps Institute for source of actual CO2 data.
