NEW YORK (AP) — Tucked between treatises on algae and prehistoric turquoise beads, the study on page 460 of a long-ago issue of the U.S. journal Science drew little attention.

“I don’t think there were any newspaper articles about it or anything like that,” the author recalls.

But the headline on the 1975 report was bold: “Are We on the Brink of a Pronounced Global Warming?” And this article that coined the term may have marked the last time a mention of “global warming” didn’t set off an instant outcry of angry denial.

In the paper, Columbia University geoscientist Wally Broecker calculated how much carbon dioxide would accumulate in the atmosphere in the coming 35 years, and how temperatures consequently would rise. His numbers have proven almost dead-on correct. Meanwhile, other powerful evidence poured in over those decades, showing the “greenhouse effect” is real and is happening. And yet resistance to the idea among many in the U.S. appears to have hardened.

What’s going on?

“The desire to disbelieve deepens as the scale of the threat grows,” concludes economist-ethicist Clive Hamilton.

He and others who track what they call “denialism” find that its nature is changing in America, last redoubt of climate naysayers. It has taken on a more partisan, ideological tone. Polls find a widening Republican-Democratic gap on climate. Republican presidential candidate Rick Perry even accuses climate scientists of lying for money. Global warming looms as a debatable question in yet another U.S. election campaign.

From his big-windowed office overlooking the wooded campus of the Lamont-Doherty Earth Observatory in Palisades, N.Y., Broecker has observed this deepening of the desire to disbelieve.

“The opposition by the Republicans has gotten stronger and stronger,” the 79-year-old “grandfather of climate science” said in an interview. “But, of course, the push by the Democrats has become stronger and stronger, and as it has become a more important issue, it has become more polarized.”

The solution: “Eventually it’ll become damned clear that the Earth is warming and the warming is beyond anything we have experienced in millions of years, and people will have to admit…” He stopped and laughed.

“Well, I suppose they could say God is burning us up.”

The basic physics of anthropogenic — manmade — global warming has been clear for more than a century, since researchers proved that carbon dioxide traps heat. Others later showed CO2 was building up in the atmosphere from the burning of coal, oil and other fossil fuels. Weather stations then filled in the rest: Temperatures were rising.

“As a physicist, putting CO2 into the air is good enough for me. It’s the physics that convinces me,” said veteran Cambridge University researcher Liz Morris. But she said work must go on to refine climate data and computer climate models, “to convince the deeply reluctant organizers of this world.”

The reluctance to rein in carbon emissions revealed itself early on.

In the 1980s, as scientists studied Greenland’s buried ice for clues to past climate, upgraded their computer models peering into the future, and improved global temperature analyses, the fossil-fuel industries were mobilizing for a campaign to question the science.

By 1988, NASA climatologist James Hansen could appear before a U.S. Senate committee and warn that global warming had begun, a dramatic announcement later confirmed by the Intergovernmental Panel on Climate Change (IPCC), a new, U.N.-sponsored network of hundreds of international scientists.

But when Hansen was called back to testify in 1989, the White House of President George H.W. Bush edited this government scientist’s remarks to water down his conclusions, and Hansen declined to appear.

That was the year U.S. oil and coal interests formed the Global Climate Coalition to combat efforts to shift economies away from their products. Britain’s Royal Society and other researchers later determined that oil giant Exxon disbursed millions of dollars annually to think tanks and a handful of supposed experts to sow doubt about the facts.

In 1997, two years after the IPCC declared the “balance of evidence suggests a discernible human influence on global climate,” the world’s nations gathered in Kyoto, Japan, to try to do something about it. The naysayers were there as well.

“The statement that we’ll have continued warming with an increase in CO2 is opinion, not fact,” oil executive William F. O’Keefe of the Global Climate Coalition insisted to reporters in Kyoto.