A comprehensive analysis of almost 40 years' worth of ExxonMobil communications has found that the company consistently misled the public on the mechanisms of climate change.

In a new peer-reviewed study investigating nearly 200 climate change documents from the oil and gas giant, researchers discovered a damning discrepancy between what the company internally acknowledged versus its public statements of denial and doubt.

"[O]n the question of whether ExxonMobil misled non-scientific audiences about climate science, our analysis supports the conclusion that it did," a team from Harvard University writes in the study.

"ExxonMobil contributed quietly to the science and loudly to raising doubts about it."

The analysis, conducted by science historians Geoffrey Supran and Naomi Oreskes, comes in response to a challenge laid down by ExxonMobil after a series of media reports in 2015 claimed the company had engaged for decades in a campaign of climate denial even while its own researchers worked to confirm the science.

"Read the documents," a company release implored.

"Go ahead, you really should. Read the documents InsideClimate News cites that purportedly prove some conspiracy on ExxonMobil's part to hide our climate science findings."

ExxonMobil argued that the claims were "based on deliberately cherry-picked statements" and "taken completely out of context".

To find out if that were the case, Supran and Oreskes combed through 187 of the company's climate change communications released between 1977 and 2014.

The trove included peer-reviewed research by ExxonMobil scientists, along with internal corporate documents, and a series of advertorial-style promotions paid to appear in The New York Times.

What they found was that as the communications became more publicly accessible, the tone on climate change – whether it was real, human-caused, and a serious issue – underwent a serious shift.

"[A]ccounting for expressions of reasonable doubt, 83 percent of peer-reviewed papers and 80 percent of internal documents acknowledge that climate change is real and human-caused," the researchers write, "yet only 12 percent of advertorials do so, with 81 percent instead expressing doubt."

The two-faced approach saw the corporation shelling out approximately $31,000 for each advertorial, which sometimes included simplified, generalised information that actually contradicted the findings of the company's own, far less accessible research that year.

"For the most part their research was highly technical, hidden behind the walls of ExxonMobil offices, or reported in academic publications with access only through a paywall," the researchers write in an op-ed piece accompanying the release of their paper.

But while the company understood the emerging science on climate change as far back as the 1970s, as recently as 1997 ExxonMobil was still sowing doubt and ambiguity unequivocally in public.

"Let's face it: The science of climate change is too uncertain to mandate a plan of action that could plunge economies into turmoil," an advertorial from that year read.

"We still don't know what role man-made greenhouse gases might play in warming the planet."

The researchers acknowledge that while textual analysis of communications is an inherently subjective field of science, they think the overall trend across this significant breadth of communications is clear.

The team emphasises their research doesn't suggest ExxonMobil suppressed, withheld, or hid climate change from the public – but that the company consistently misled people about global warming and what was causing it, and did so for decades, even knowing what they knew.

"We found that they were really good scientists," Oreskes told John Schwartz at The New York Times.

"That finding then makes the contrast with the advertorials that much more notable."

The findings are reported in Environmental Research Letters.