The results of an eight-month investigation by InsideClimate News, published Wednesday, show that Exxon scientist warned company executives decades ago about human-caused global warming.

But despite its own 40-year-old research that showed that burning fossil fuels released carbon dioxide that was warming the planet to harmful levels, Exxon – the United States' largest oil company – has spent $30 million to discredit climate science to protect its carbon-based business.

In 1977, senior Exxon scientist James F. Black told company executives, "In the first place, there is general scientific agreement that the most likely manner in which mankind is influencing the global climate is through carbon dioxide release from the burning of fossil fuels," according to InsideClimate.

"Present thinking," Dr. Black then estimated in 1978, "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."

Despite the warnings, the oil giant, which brought in $127 billion in gross profit in 2014, cut back its carbon dioxide research in the late 1980s when – like today – a glut of oil depressed its price, hurting the company's business. In the ensuing decades, Exxon instead focused on casting doubt on global warming warnings and lobbying against international action to control greenhouse gas emissions.

It spent $1 million on climate denial groups in 2014 alone, reports environmental advocacy group Greenpeace.

A few decades ago, things were different. Exxon was at the forefront of climate research. The company’s research and engineering division comprised a team of accomplished scientists and mathematicians who worked with university scientists and the US Department of Energy to develop sophisticated climate models. They spent three years and at least $1 million measuring the levels of CO 2 in the air and ocean aboard the company’s Esso Atlantic tanker, the InsideClimate report explains.

Exxon scientists published their research in peer-reviewed science journals.

By 1982, company scientists reported to management that despite the need for more research, controlling global warming “would require major reductions in fossil fuel combustion.”

According to InsideClimate:

Unless that happened, "there are some potentially catastrophic events that must be considered," the primer said, citing independent experts. "Once the effects are measurable, they might not be reversible."

InsideClimate's review of corporate financial reports filed during the height of the company’s climate research era showed that the company did not relay the gloomy results to shareholders.

By the mid 1980s, in the days of a major recession triggered by an oil crisis, global warming became a topic of national discourse.

“With alarm bells suddenly ringing,” reports InsideClimate, “Exxon started financing efforts to amplify doubt about the state of climate science.

Today, Exxon acknowledges climate change is a "risk," though it doesn't believe that reducing the use of fossil fuels is the right way to mitigate it.

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“It is equally essential that society manages the risk of climate change by increasing energy efficiency and by investing in research into technologies to reduce greenhouse gas emissions,” a 2014 company announcement says.

But, the company says, “All energy sources, including carbon-based fuels, are necessary to meet future global energy demand growth as society manages the risks of climate change.”