Despite its efforts for nearly two decades to raise doubts about the science of climate change, newly discovered company documents show that as early as 1977, Exxon research scientists warned company executives that carbon dioxide was increasing in the atmosphere and that the burning of fossil fuels was to blame.

The internal records are detailed in a new investigation published Wednesday by InsideClimate News, a Pulitzer Prize-winning news organization covering energy and the environment.

The investigation found that long before global warming emerged as an issue on the national agenda, Exxon formed an internal brain trust that spent more than a decade trying to understand the impact of rising CO2 levels in the atmosphere — even launching a supertanker with custom-made instruments to sample and understand whether the oceans could absorb the rising atmospheric CO2 levels. Today, Exxon says the study had nothing to do with CO2 emissions, but an Exxon researcher involved in the project remembered it differently in the below video, which was produced by FRONTLINE in association with the InsideClimate News report.

In 1978, the Exxon researchers warned that a doubling of CO2 levels in the atmosphere would increase average global temperatures by 2 to 3 degrees Celsius and would have a major impact on the company’s core business. “Present thinking holds that man has a time window of five to ten years before the need for hard decisions regarding changes in energy strategies might become critical,” one scientist wrote in an internal document.

The warnings would later grow more urgent. In a 1982 document marked “not to be distributed externally,” the company’s environmental affairs office wrote that preventing global warming would require sharp cuts in fossil fuel use. Failure to do so, the document said, could result in “some potentially catastrophic events” that “might not be reversible.”

Some on the Exxon internal research team saw the potential for a greater impact in their work. “This may be the kind of opportunity that we are looking for to have Exxon technology, management and leadership resources put into the context of a project aimed at benefitting mankind,” Harold N. Weinberg, an Exxon manager, wrote in a March 1978 internal memo.

But in the mid-1980s, collapsing oil prices, among other pressures, pushed Exxon to change course, according to the Inside Climate News investigation, widening a gulf between its research arm and the company’s executive suite. The report notes that by the 1990s:

Exxon helped to found and lead the Global Climate Coalition, an alliance of some of the world’s largest companies seeking to halt government efforts to curb fossil fuel emissions. Exxon used the American Petroleum Institute, right-wing think tanks, campaign contributions and its own lobbying to push a narrative that climate science was too uncertain to necessitate cuts in fossil fuel emissions.

“Let’s agree there’s a lot we really don’t know about how climate change will change in the 21st century and beyond,” Lee Raymond, the company’s former chairman and chief executive officer told an audience in a 1997 speech to the World Petroleum Conference.

In a written response to the InsideClimate News investigation, an Exxon spokesman said that, “At all times, the opinions and conclusions of our scientists and researchers on this topic have been solidly within the mainstream of the consensus scientific opinion of the day and our work has been guided by an overarching principle to follow where the science leads. The risk of climate change is real and warrants action.”

While it’s impossible to know where the climate change debate would be today without Exxon’s early decision to shift course on the science, the about-face was a lost opportunity in the overall effort to slow the rise of CO2 emissions, according to one climate researcher interviewed by InsideClimate News.

“All it would have taken is for one prominent fossil fuel CEO to know this was about more than just shareholder profits, and a question about our legacy,” said Michael Mann, the director of the Earth System Science Center at Pennsylvania State University. “But now because of the cost of inaction — what I call the ‘procrastination penalty’ — we face a far more uphill battle.”