As delegates from 195 countries gather in Paris for the U.N. Climate Conference, it seems public sentiment towards climate change has shifted.

Sixty-three percent of Americans think climate change is a problem, according to the latest Washington Post/ ABC News poll, a drop from 69 percent a year ago. Currently 36 percent say climate change is not a serious problem at all.

This change in attitude has been reflected in the rhetoric of many politicians. Presidential candidate Donald Trump recently told CNN that he is not “a believer in climate change.

The impassioned nature of the debate is partly tied to corporate funding of climate change skeptics, according a study published this week in Nature Climate Change. Justin Farrell, author of the study and a professor at the Yale School of Forestry & Environmental Studies, notes a strong connection between companies like ExxonMobile and publications that deny climate change.

His study examined the network of about 4,500 individuals and the 164 related organizations that actively dispute climate change. He found that the largest sources of funding for climate change deniers came from Exxon and the Koch brothers’ family foundations.

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Funding climate denial research meant that their "efforts were able to move into the mainstream media," says Robert Brulle, professor of sociology at Drexel University. "The think tanks’ efforts to get the media to cover [climate change denial] has systematically affected the nature of reporting on climate change."

Last year, Exxon reportedly spent $2.5 million on political candidates and advocacy groups that deny climate change.