Study highlights link between corporate funds and voices stirring doubt over human role in warming planet.

Climate change has long been a highly polarising topic in the United States, with Americans lining up on opposite sides depending on their politics and worldview. Now a scientific study sheds new light on the role played by corporate money in creating that divide.

The report, a systematic review of 20 years' worth of data, highlights the connection between corporate funding and messages that raise doubts about the science of climate change and whether humans are responsible for the warming of the planet. The analysis suggests that corporations have used their wealth to amplify contrarian views and create an impression of greater scientific uncertainty than actually exists.

"The contrarian efforts have been so effective for the fact that they have made it difficult for ordinary Americans to even know who to trust," said Justin Farrell, a Yale University sociologist and author of the study, released yesterday in the peer-reviewed journal, Proceedings of the National Academy of Science.

Numerous previous studies have examined how corporate-funded campaigns have helped shape individual views about global warming. But the Yale study takes what Farrell calls the "bird's-eye view", using computer analytics to systematically examine vast amounts of printed matter published by 164 groups - including thinktanks and lobbying firms - and more than 4500 individuals who have been sceptical of mainstream scientific views on climate change.

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The study analysed the articles, policy papers and transcripts produced by these groups over a 20-year period. Then it separated the groups that received corporate funding from those that did not.

The results, Farrell said, revealed an "ecosystem of influence" within the corporate-backed groups. Those that received donations consistently promoted the same contrarian themes - casting doubt, for example, on whether higher levels of man-made carbon-dioxide in the atmosphere were harmful to the planet. There was no evidence of such co-ordination among the non-funded groups.

The existence of corporate money "created a united network within which the contrarian messages could be strategically created" and spread, Farrell said.

"This counter-movement produced messages aimed, at the very least, at creating ideological polarisation through politicised tactics, and at the very most, at ... refuting current scientific consensus with scientific findings of their own," he said.

The report did not examine the impact of outside money on the messages of groups that encourage activism on climate change. Farrell suggested that there were qualitative differences between such groups and those that sought to advance corporate interests by promoting scepticism about science.

"Funders looking to influence organisations who promote a consensus view are very different from funders looking to influence organisations who have the goal of creating polarisation and controversy and delaying policy progress on a scientific issue that has nearly uniform consensus," he said.

The publication of the report comes two weeks after New York prosecutors announced an investigation into whether ExxonMobil misled the public and investors about the risks of climate change. The probe was prompted in part by reports in the Los Angeles Times and the online publication Inside Climate News, alleging that Exxon researchers expressed concerns about climate change from fossil fuel emissions decades ago, even as the company publicly raised doubts about whether climate-change was scientifically valid.

Exxon has declined to comment on the investigation while acknowledging that its position on climate change has evolved in recent years. "Our company, beginning in the latter part of the 1970s ... has been involved in serious scientific research, and we have been supporting since that time scientific understanding of the risk of climate change," Exxon's vice-president of public and government affairs Ken Cohen told reporters after the New York probe was revealed.