A study published Wednesday asserts that Exxon Mobil Corp. misled the public for years about what it knew regarding the science of climate change.

The findings from a pair of Harvard University researchers add to charges from environmentalists, Democratic attorneys general and others that Exxon knew decades ago that its fossil fuels harmed the planet but chose to sow doubt about the science to the public and investors.

The new peer-reviewed study, published in Environmental Research Letters, relies heavily on textual content analysis, a sociological process meant to systematically read texts for patterns or other wide-ranging findings.

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“We conclude that ExxonMobil misled the public,” the researchers write. “We stress that the question is not whether ExxonMobil ‘suppressed climate change research,’ but rather how they communicated about it.”

The authors, Geoffrey Supran and Naomi Oreskes, specialize in scientific inquiry. Oreskes is an outspoken critic of climate change skeptics and others who disagree with the scientific consensus on climate.

The study, analyzing Exxon’s external and internal statements from 1977 through 2014, found that the widest gulf between Exxon’s public and private communication was between paid “advertorials” the company wrote and all other documents studied.

While 83 percent of its peer-reviewed papers and 80 percent of internal documents acknowledged humans' role in climate change, only 12 percent of its advertorials did, and 81 percent of them expressed doubt.

Exxon slammed the Wednesday study in a statement, pointing out that it was sponsored in part by the Rockefeller Family Fund, which has funded other previous efforts to show Exxon misled on climate.

“The study was paid for, written and published by activists leading a five-year campaign against the company,” Exxon said in a statement. “It is inaccurate and preposterous. Rather than pursuing solutions to address the risk of climate change, these activists, along with trial lawyers, have acknowledged a goal of extracting money from our shareholders and attacking the company’s reputation.”

Exxon now publicly agrees with the scientific consensus that greenhouse gases from human activity are the main cause of climate change, and the company supports a tax on carbon dioxide emissions.

It has also repeatedly denied charges that it lied to the public or investors.

Green groups said the research is a significant addition to the case that Exxon lied.

“Exxon has officially run out of excuses,” Naomi Ages, Greenpeace’s lead climate liability campaigner, said in a statement.

“This peer-reviewed study from Harvard is just the latest piece of evidence indicating that the largest oil company in the world knew about the risks of climate change, but concealed them from the public and shareholders. State attorneys general dedicated to protecting people and the environment from recent assaults should act now to hold polluters accountable for the biggest crisis facing humanity.”