NEW YORK – 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.

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 proved 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.

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

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.

Evidence mounts

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.

By 2000, the CO2 built up in the atmosphere to 369 parts per million – just 4 ppm less than Broecker predicted – compared with 280 ppm before the industrial revolution.

Global temperatures rose as well, by 1.1 degrees F in the 20th century. The decade 2000-2009 was the warmest on record, and 2010 and 2005 were the warmest years on record.

Satellite and other monitoring, meanwhile, found nights were warming faster than days, and winters more than summers, and the upper atmosphere was cooling while the lower atmosphere warmed – all clear signals greenhouse warming was at work, not some other factor.

The impact has been widespread.

An authoritative study this August reported that hundreds of species are retreating toward the poles, egrets showing up in southern England, American robins in Eskimo villages.

The heat is cutting into wheat yields, nurturing beetles that are destroying northern forests, attracting malarial mosquitoes to higher altitudes.

From the Rockies to the Himalayas, glaciers are shrinking, sending ever more water into the world’s seas. Because of accelerated melt in Greenland and elsewhere, the eight-nation Arctic Monitoring and Assessment Program projects ocean levels will rise 35 to 63 inches by 2100, threatening coastlines everywhere.

The oceans are turning more acidic, too, from absorbing excess carbon dioxide.

Resistance political

In the face of years of scientific findings and growing impacts, the doubters persist.

They ignore long-term trends and seize on insignificant year-to-year blips in data to claim all is well. They focus on minor mistakes in thousands of pages of peer-reviewed studies to claim all is wrong. And they carom from one explanation to another for today’s warming Earth: jet contrails, sunspots, cosmic rays, natural cycles.

“Ninety-eight percent of the world’s climate scientists say it’s for real, and yet you still have deniers,” observed former U.S. Rep. Sherwood Boehlert, a New York Republican who chaired the House’s science committee.

The Australian scholar Hamilton sought to explain why in his 2010 book, “Requiem for a Species: Why We Resist the Truth About Climate Change.”

In an interview, he said he found a “transformation” from the 1990s and its industry-financed campaign, to an America where climate denial “has now become a marker of cultural identity in the ‘angry’ parts of the United States.”

“Climate denial has been incorporated in the broader movement of right-wing populism,” he said, a movement that has “a visceral loathing of environmentalism.”

An in-depth study of a decade of Gallup polling finds statistical backing for that analysis.

On the question of whether they believed the effects of global warming were already happening, the percentage of self-identified Republicans or conservatives answering “yes” plummeted from almost 50 percent in 2007-2008 to 30 percent or less in 2010, while liberals and Democrats remained at 70 percent or more, according to the study in this spring’s Sociological Quarterly.

Al Gore, for one, remains upbeat. The former vice president and Nobel Prize-winning climate campaigner says “ferocity” in defense of false beliefs often increases “as the evidence proving them false builds.”

In an AP interview, he pointed to tipping points in recent history – the collapse of the Berlin Wall, the dismantling of U.S. racial segregation – when the potential for change built slowly in the background, until a critical mass was reached.

“This is building toward a point where the falsehoods of climate denial will be unacceptable as a basis for policy much longer,” Gore said.

“As Dr. Martin Luther King Jr. said, ‘How long? Not long.’ ”