Climate skeptics say polar bears are fine. Scientists beg to differ.

Furry, button-nosed and dependent on sea ice for their survival, polar bears have long been poster animals for climate change.

But at a time when established climate science is being questioned at the highest levels of government, climate denialists are turning the charismatic bears to their own uses, capitalizing on their symbolic heft to spread doubts about the threat of global warming.

The scientific evidence that the polar bear's Arctic home is warming twice as fast as the rest of the planet is overwhelming, supported by reports like the National Climate Assessment, which was compiled by 13 federal agencies. In some Arctic regions, scientists have documented declines in polar bear numbers and disturbing signs of physical deterioration linked to the loss of sea ice. And last year, the Obama administration called human-driven climate change the biggest threat to the bears' continued existence.

But to hear climate denialists tell it, polar bears are doing just fine. On Watts Up With That, Climate Depot and other websites that dispute climate science, bloggers insist that the Arctic's receding ice is part of a natural warming cycle unrelated to human activities. Predictions about devastating declines in polar bear populations, they say, have failed to materialize.

[As sea ice gets scarcer, polar bear attacks on people become more frequent]

In effect, many scientists say, the bears have been co-opted by climate denialists, and in an article published Tuesday in the peer-reviewed journal BioScience, 14 prominent researchers argue that denialist blogs with wide followings are using the bears to spread misinformation about the causes and consequences of climate change.

The researchers also singled out Polar Bear Science, a blog run by Susan J. Crockford, a Canadian zoologist, as a primary source of dubious information about the status of polar bears. About 80 percent of the contrarian websites the researchers studied referred to Crockford's blog as a primary source, they said.

The publication of the article is likely to intensify a furor in contrarian circles that began four months ago after an "early view" version of the paper appeared on the BioScience website.

The reaction was swift and fierce. A post on Climate Audit, a blog popular with climate skeptics, called the article "a hit piece" and dismissed it as "yet another piece of propaganda to push a Climate Change agenda." The Global Warming Policy Foundation, a pro-fossil fuel think tank in Britain that has published briefing papers by Crockford, chimed in with the headline, "14 Climate Bullies Attack Susan Crockford for Telling the Truth About Polar Bears."

Crockford tweeted that the article amounted to "academic rape" and demanded that it be retracted.

The authors of the paper also came under fire. Freedom of information requests were filed at universities for three of the authors' correspondence, with at least one request by Crockford. (Two of the requests have been turned down, while one, at the University of California, Davis, is still under review.) And Hans LaBohm, editor of the blog ClimateGate.nl, wrote to the Royal Netherlands Academy of Arts and Sciences demanding that Jeffrey A. Harvey, an ecologist and the article's lead author, be reprimanded for conduct "unworthy of serious scientists."

Harvey said the paper grew out of the increasing frustration he and other scientists felt about the spread of false information, the disregard of established evidence and the harassment of researchers that has in some cases accompanied the public debate on climate change.

By contesting scientific findings about polar bears, denialists hope to instill doubt about climate science as a whole, Harvey said. "Every time these deniers make some outlandish claim in the media and we don't respond to it, it's like a soccer match and we've given them an open goal," he added.

Michael Oppenheimer, a professor of geoscience and international affairs at the Woodrow Wilson School at Princeton who was not involved with the article, said he was not surprised to see scientists banding together against climate change denial.

"Some climate scientists basically have had enough of being punching bags," Oppenheimer said.

He added that scientists have a right to publicly question someone's expertise, as the authors did with Crockford. "If people are going to make claims that are contrary to scientific understanding, then it's perfectly appropriate to call them out for it," he said, "because in this day and age, where there are so many information sources, it's often difficult to identify who's a real expert."

Although many contrarian websites pick up discussion about polar bears from Crockford's blog, the article noted that she has no demonstrated expertise in climate science or its effects on polar bears. The credentials of many of the BioScience paper's authors include long lists of published, peer-reviewed articles and studies on these subjects.

[Emaciated polar bear in viral video is a warning, but not necessarily a climate victim]

An adjunct professor in anthropology at the University of Victoria in British Columbia, Crockford's fields of study include evolution and paleoecology. She has published some peer-reviewed articles that touch on polar bears. She has also published reports and articles that have not been peer-reviewed, like those through the Global Warming Policy Foundation.

Scott Collins, BioScience's editor-in-chief, said the journal took Crockford's demand for retraction seriously but "determined that there was no grounds to do so." The final version, Collins said, includes "corrections that slightly change two sentences," in one case narrowing a statement about Crockford's credentials to specify that her lack of expertise is in "the effects of sea ice on the population dynamics of polar bears."

Crockford declined to be interviewed by phone or answer questions in writing. But she said in an email: "This paper is a smack-talk response to my pointing out that polar bear numbers did not plummet as predicted when mid-centurylike sea ice conditions arrived unexpectedly in 2007. The paper is not only devoid of science, it lacks the professional decorum that other science journals demand."

Steven C. Amstrup, an author of the paper and chief scientist for Polar Bears International, a conservation group, said Crockford frequently referenced a 2007 report he prepared when he was the federal government's polar bear project director in Alaska. The report projected that if the rise of global temperature continued unabated, two-thirds of the world's polar bears could be lost by the middle of this century.

By that time, climate models suggest, September sea ice in the Arctic could decline to an area of 1 million square kilometers or less. Scientists have estimated that in the 19th and 20th centuries, the average September sea ice extent was 8 million square kilometers.

But Crockford often asserts on her blog that sea ice has already declined to the projected midcentury levels and that the polar bear population has not decreased by two-thirds.

Amstrup, however, said that according to the National Snow and Ice Data Center, the average September sea ice extent for the years 2007 to 2017 was 4.5 million square kilometers, "nowhere near the low levels projected it would be by the middle of the century."

"To say that we already should have seen those declines now when we're not nearly to the middle of the century yet is absurd," he said.

Mainstream scientists are in agreement that polar bear numbers will decline drastically as Arctic sea ice disappears, since the bears use the ice as a platform to hunt seals. Studies have found disturbing changes in the bears' physical condition, body size, reproduction and survival rates, some of which have been linked to sea ice loss and more ice-free days.

Of the 19 polar bear subpopulations in the Arctic Circle, three have shown substantial declines, including bears in the South Beaufort Sea off Alaska's coast and in West Hudson Bay in Canada. One subpopulation has increased in numbers, and scientists know little or nothing about nine of the others, which are either in Russian territory or in locations so remote that resources are not available for surveys.

The paper's authors wrote that contrarian blogs tend to focus on single data points or to emphasize gaps in scientific knowledge, "suggesting that those uncertainties cast doubt on the present and future demographic trends of polar bears."

Andrew Derocher, a biology professor at the University of Alberta who has studied polar bears for 20 years and was not involved in the paper, said in his view, the contrarians were completely missing the big picture. The issue, he said, boiled down to something simple: Polar bears need sea ice.

"It's just a habitat loss issue," Derocher said. "There's nothing more complicated than that."