In our series, "Exxon: The Road Not Taken," InsideClimate News published several dozen documents that established the arc of Exxon's pioneering yet little-known climate research, which began 40 years ago.

Our reporting team chose them from the thousands of mainly internal company documents that we reviewed in our 10-month investigation.

In addition to the ones we have already published since September—which ExxonMobil has now downloaded from the ICN website and imported to its blog—there are more worth sharing.

Each illuminates a nuance of Exxon's early internal discussions about climate change, from interactions at the highest echelons to presentations for the rank-and-file. The documents reveal the contrast between Exxon's initial public statements about climate change and the company's later efforts to deny the link between fossil fuel use and higher global temperatures.

A selection of previously unpublished memos and reports are included and explained here, as part of ICN's continuing exploration of Exxon's climate documents.

Exxon Senior Vice President Weighs in on the 'Greenhouse Program' (1980)

This memo from June 9, 1980, indicates that carbon dioxide research was not a project that Exxon's board simply greenlighted. It was an issue so important that at least one senior vice president was paying close attention to the science, and he was interested and versed enough to argue its arcana.

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On June 9, 1980, Harold N. Weinberg, a top manager in Exxon Research and Engineering, the hub of the company's carbon dioxide research, sent a note to Richard Werthamer and Henry Shaw with the subject, "Greenhouse Program," the company's CO 2 research initiative. Shaw was the unit's lead climate researcher at the time, Werthamer his boss.

In the note, Weinberg wrote that he gave a presentation at a June 4 meeting about the program and said, "George Piercy questioned me closely on the statement that there is a net CO 2 flux out of the ocean at the upwelling zones."

At the time, Exxon had deployed a state-of-the-art supertanker outfitted with equipment for measuring marine CO 2 concentrations to understand the role the oceans play in the world's carbon cycle. Scientists knew that the oceans had absorbed some of the carbon dioxide released from the increased global consumption of fossil fuels. But Exxon's researchers wanted to understand how exactly CO 2 behaved in the oceans—and whether after trapping the gas, the seas would eventually release it into the atmosphere.

Piercy was a senior vice president at Exxon in 1980, and a member of the board of directors. According to the note, he challenged Weinberg's assertion that global circulation patterns move CO 2 out of the deep oceans to the surface where it escapes into the atmosphere, a process known as "upwelling."

Piercy disagreed, arguing the oceans can hold higher concentrations of CO 2 without releasing it into the air. (As it turns out, Weinberg was right, though overall, the world's oceans act as a global sink, pulling CO2 from the air into the water and helping dampen the effects of climate change.)

Other memos from the early 1980s (here and here) show that ER&E staff regularly apprised at least one other senior vice president, M.E.J. O'Loughlin, of the latest climate research, too.

Exxon's Lead Climate Researcher Presents: The Company's Position on the CO 2 Greenhouse Effect (1981)

In this May 15, 1981 memo, Exxon estimates a 3-degree Celsius rise in global average temperatures in 100 years, and appears ready to discuss publicly that a time could arrive when the world would have to shift to renewable energy. Exxon thought such a transition could happen in a gradual, "orderly" way.

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By 1981, Exxon had already established itself as a leader on the greenhouse effect with many in industry and the government. In early May of that year, Henry Shaw prepared a "brief summary of our current position on the CO 2 Greenhouse effect" for Edward E. David, Jr., president of Exxon Research and Engineering, in case the topic came up at an Exxon symposium in San Francisco where David would be speaking.

Based on documentary evidence, it appears the summary went through several drafts and the final version went to David's office on May 15.

The bullet points that Shaw presented to David start with the idea that "there is sufficient time to study the problem before corrective action is required." Shaw based his caution on estimates that higher global temperatures caused by rising CO 2 would only be felt around the year 2000, and that CO 2 concentrations in the atmosphere would double in about 100 years. Those gaps, Shaw wrote, permit "time for an orderly transition to non-fossil fuel technologies should restrictions on fossil fuel use be deemed necessary."

The document did not raise doubts about the links between fossil fuel use, higher CO 2 concentrations and a warmer planet. Shaw wrote:

• "Atmospheric CO 2 will double in 100 years if fossil fuels grow at 1.4%/ a2.

• 3oC global average temperature rise and 10oC at poles if CO 2 doubles.

—Major shifts in rainfall/agriculture

—Polar ice may melt"

Eleven other staff and managers at Exxon Research, besides David, were sent the paper with the corporate position on global warming that Shaw had articulated.

By the end of the 1980s, Exxon would publicly pivot away from open consideration of any restrictions on fossil fuel use because of its effect on the atmosphere.

In 1996, when climate research was more certain about the link between fossil fuel combustion and climate change than during the time of Shaw's memo, Exxon's new chairman and chief executive Lee Raymond said in a speech in Detroit: "Currently, the scientific evidence is inconclusive as to whether human activities are having a significant effect on the global climate."

At Exxon's annual meeting in 2015, chairman Rex Tillerson said it would be best to wait for more solid science before acting on climate change. "What if [after] everything we do, it turns out our models are lousy, and we don't get the effects we predict?"

A Presentation on 'CO 2 Greenhouse and Climate Issues' (1984)

Exxon began incorporating CO 2 estimates into its corporate planning as early as 1981, this March 28, 1984 presentation shows. The company acknowledged the link between fossil fuel use and climate change throughout most of the 1980s.

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In 1984, Shaw no longer ran Exxon's CO 2 research. He had been moved from that post a few years earlier as the company shifted its focus from the expensive empirical research on the tanker to cheaper, yet still highly significant, climate modeling. By the mid-1980s, Shaw worked on keeping track of emerging independent climate research and apprising top managers.

On March 28, Shaw gave a presentation at an internal Exxon environmental conference in Florham Park, N.J. He showed projections of fossil fuel use through the 21st century and the growth in global carbon dioxide expected from it.

Shaw told his audience that he was regularly asked to prepare estimates for Exxon about CO 2 from fossil fuel use. Those estimates used and were integrated into the company's energy projections for the 21st century and circulated within Exxon.

He wrote in the presentation: "As part of CPPD's technology forecasting activities in 1981, I wrote a CO 2 greenhouse forecast based on publically available information. Soon thereafter, S&T [Science & Technology] requested an update of the forecast using Exxon fossil fuel projections. This request was followed late in 1981 with a request by CPD [Corporate Planning Department] for assistance in evaluating the potential impact of the CO 2 effect in the '2030 Study.' After meeting CPD's specific need, a formal technology forecast update was issued to S&T in the beginning of April 1982. It was subsequently sent for review to the Exxon affiliates."

Exxon's affiliates are the company's various divisions, including exploration and production, refining, international units and shipping.

Then Shaw shared with his audience estimates by Exxon and three other entities—the Environmental Protection Agency, the National Academy of Sciences, and the Massachusetts Institute of Technology—about when CO 2 would double in the atmosphere, what kind of increases could occur in average global temperatures and the effects of such changes on human life.

Exxon estimated that CO 2 would double by 2090, which was later than what the other groups had projected. It estimated that average global temperatures would rise by 1.3 to 3.1 degrees Celsius (2.3 to 5.6 degrees Fahrenheit), which was in the mid-range of the four projections that Shaw shared.

Shaw showed the policy recommendations of the three organizations and Exxon to address climate change. According to him, MIT argued for an "extreme reduction in fossil fuel use," while the others, including Exxon, urged a more cautious approach. But Exxon did not deny the link between fossil fuel use and climate change as it would begin to do just five years later.

ICN reporter Lisa Song contributed to this report.