WASHINGTON -- When former NASA administrators, astronauts and engineers released a letter earlier this week attacking the science of climate change, its veneer of legitimacy kicked off a media blitz. Yet none of the letter's 49 signatories are climate scientists, and with more than 18,000 people currently working for NASA, to say nothing of the tens of thousands more who are retired, the letter seems more than anything like an empty publicity stunt, and one for which there's considerable precedent.

"When you have an area of the science where there is a consensus like in climate change, where the problem is real and the scientific implications are on a collision course with vested interests like the fossil fuel industry, you often see this," said Michael Mann, a well-known climate scientist and Penn State professor.

NASA has been clear that it firmly accepts the reality of the science behind climate change, including the work of renowned climate scientist James Hansen, so complaints from a few dozen retired NASA administrators and a handful of astronauts and engineers calling on NASA to stop saying that anthropogenic carbon dioxide causes climate change can hardly be taken seriously.

A full 98 percent of all working climate scientists affirm anthropogenic climate change, according to a paper published in 2010 in the Proceedings of the National Academies of Sciences, and the Intergovernmental Panel on Climate Change has found the evidence that the world is warming to be "unequivocal."

"They can't discredit the science in the legitimate sphere of scientific debate, which is to say, the peer-reviewed literature, the various assessment reports published by various governments ... so what they try to do is create the illusion that the science is being hotly contested by finding the small group, often of curmudgeonly individuals, who might feel left out," said Mann, who documents this recurrent phenomenon in his newly released book, "The Hockey Stick And The Climate Wars: Dispatches From The Front Lines."

Author John Cook similarly considers such public announcements as one of the five most easily identifiable characteristics of science denialism, wherein deniers use fake experts to undermine established science.

"These are individuals purporting to be experts but whose views are inconsistent with established knowledge," writes Cook. "Fake experts have been used extensively by the tobacco industry who developed a strategy to recruit scientists who would counteract the growing evidence on the harmful effects of second-hand smoke."

The stunts gain traction in part because it can be hard for non-experts to determine what is and what isn't legitimate criticism. Evolutionary biologists, who've long had to contend with such attacks, have parodied the trickery with "Project Steve," a media stunt in which they collected the signatures only of evolutionary biologists named Steve to demonstrate how easy it is to round up a group people who'll sign on to just about anything.

There's a long history of climate deniers who write such letters (their preferred vehicle) to voice their discontent. The much-discussed Oregon Petition has been repeatedly debunked, with both the scientific credentials and the authenticity of its signatories' names being called into question. When Scientific American took a random sample of 30 of the 1,400 signatories, for instance, only "11 said they still agreed with the petition -- one was an active climate researcher, two others had relevant expertise, and eight signed based on an informal evaluation. Six said they would not sign the petition today, three did not remember any such petition, one had died, and five did not answer repeated messages."

Another effort, known as the Wall Street Journal 16, urged people not to take any actions to address climate change. Spearheaded by Harrison Schmitt, who also helped organize this week's letter from former NASA employees, the op-ed boasted only two climate scientists who'd published climate research in the past three decades. What's more, nearly half of the 16 scientists on the list had received fossil fuel industry funding, according to Skeptical Science.

In 1995 the so-called Leipzig Declaration sought to refute the claim that there's scientific consensus on global warming and offered its stated opposition to global warming science as a reason to defy the Kyoto Protocol, which, the deniers argued, imposed unfair burdens on industrialized nations. The wording of the declaration mirrors wording in the 1992 "Statement by Atmospheric Scientists on Greenhouse Warming," which described the climate science findings as "highly uncertain" while also arguing an increase in carbon dioxide would have "beneficial effects on most crops."

Mann -- who, having survived the phony Climategate scandal, has as much experience as anyone in fighting off the political attacks of climate deniers -- offered a bit of media bait of his own.

"What's really telling is that they couldn't get people like Buzz Aldrin -- or for that matter John Glenn -- to sign this petition," Mann said. "I think it speaks volumes that the most prominent astronauts were completely uninterested in having any part in this ploy, and I was proud of them for that."