Watch Climate of Doubt on PBS. See more from FRONTLINE.

If you think Mitt Romney’s recent threats against PBS were actually about budgets or Big Bird, think again. The reason the right hates PBS is that sometimes it commits the unpardonable sin of journalism.

“Climate of Doubt,” a “Frontline” documentary that aired Tuesday night on PBS, explores how a movement mobilized to undermine public acceptance of the scientific consensus on global warming and on how human activity contributes to climate change. The conservative Heartland Institute, which has played a prominent role in seeking to discredit climate science, pre-emptively issues a statement denying that a scientific consensus exists and predicting that the documentary will be unfair.

Four years ago, the presidential candidates agreed that climate change was a critical issue demanding urgent attention. But that national call to action has disappeared and in the past four years public opinion on the issue of climate has cooled. This election cycle, the presidential candidates barely discuss climate change. New studies find that only about half of Americans believe global warming is caused by human activity. What’s behind this dramatic reversal? In Climate of Doubt, Frontline correspondent John Hockenberry of PRI’s The Takeaway explores the inner workings of the movement that changed the debate on climate change.

In numerous interviews that took him across the country, Hockenberry discovers how climate skeptics mobilized, built their argument, and undermined public acceptance of a global scientific consensus. Tim Phillips, President of Americans for Prosperity, explains how the movement was able to find a voice and gain momentum as the economy failed, “We got up a hot-air balloon, put a banner on the side of it that said, cap-and-trade means higher taxes, lost jobs, less freedom. And we went all over the country doing events and stirring up grassroots anger and frustration, concern.”

"Climate of Doubt" describes the individuals and groups behind an organized effort to attack science by undermining scientists, and to unseat politicians who say they believe there is current climate change caused by human activity. Andrew Dessler, a climate scientist at Texas A&M, says, “I fully expect that after this program airs I’ll get another FOIA request for all of my emails with you. And you know, I’ll just deal with that. As a climate scientist, I think a lot about the future. It goes with the job. And I want to make sure that in 50 years or 100 years or 200 years, nobody could ever say we didn’t warn them.”

Frontline also investigates the funding that powers the skeptic movement in the name of free market, anti-regulation, small government causes. Hockenberry finds that funding has shifted away from fossil fuel companies to more ideological, and less public sources. According to Robert Brulle, a sociologist studying the funding patterns of these groups, “The major funders of the climate counter-movement are ideologically driven foundations that are very much concerned about conservative values and world views.”