Harvard University researchers say Exxon Mobil has intentionally misrepresented climate science.

Researchers Geoffrey Supran and Naomi Oreskes have reviewed 187 documents, including internal memos and peer-reviewed papers by Exxon scientists, against ‘advertorials’ run in The New York Times.

The researchers applied methods from social science to turn statements in the documents into data points for comparison.

Mr Supran and Ms Oreskes claim that as early as 1979, Exxon scientists knew burning fossil fuels added carbon dioxide to the atmosphere and caused global temperatures to rise.

However, the company's position in newspaper ads consistently asserted doubt about climate science.

The study was funded by the group behind a campaign to prove Exxon knew more than it publicly admitted about climate change, under the slogan #ExxonKnew.

Exxon spokesperson Scott Silvestri said the study is “inaccurate and preposterous” and that the researchers were clearly looking for ways to attack the company’s reputation.

“Our statements have been consistent with our understanding of climate science,” he said.

Ms Oreskes said the study came about after Exxon’s responses to reports in InsideClimate News and The Los Angeles Times in 2015.

“They accused the journalists of cherry-picking,” Ms Oreskes said of Exxon's responses.

“They also posted a collection of documents on their website.

“They said; ‘Read the documents and make up your own mind’.

“We thought that was an excellent opportunity.”

The researchers pointed to an Exxon advertorial from 2000 that claimed a US government report on climate change was putting the “political cart before the horse” and was “based on unreliable models”.

Mr Silvestri pointed to two advertorials that Exxon placed in The New York Times that same year, which he says show the company was not creating doubt on climate change.

One statement read: “Enough is known about climate change to recognise it may pose a legitimate long-term risk and that more needs to be learned about it”.

The Harvard researchers’ paper is accessible here.