Correction: An earlier version of this article misstated the last name of the chairman of the George C. Marshall Institute. This version has been updated.

Everybody talks about the weather, as Mark Twain is famously quoted as saying, but nobody does anything about it.

Many climate researchers are no longer following that adage, noted Michael McPhaden, president of the American Geophysical Union. “Scientists today, they don’t just want to talk about it. They want to do something about it,” he said in an interview. “We’re the trustees of information which, in many ways, is of critical benefit to society.”

Some researchers are taking on a greater advocacy role to confront what many of them consider an existential crisis. But this strategy carries inherent risks, since scientists’ influence stems from the public perception that their credibility is beyond reproach.

That’s why many in the scientific community recoiled when Peter Gleick, a respected hydrologist, admitted he had tricked the Heartland Institute , a free-market think tank that questions whether human activity contributes to global warming.

“Integrity is the source of every power and influence we have as scientists,” said Peter Frumhoff, director of science and policy at the Union of Concerned Scientists. “We don’t have the power to make laws, or run the economy.”

Georgia Institute of Technology atmospheric scientist Judith Curry says human activity is contributing to climate change but it remains uncertain whether it is or will be “the dominant factor.” She said she respects Gleick’s scientific work but worries about where his activism has taken him.

“Colleagues trying to make criminals out of themselves, and each other, is just an insane situation,” she said.

The stakes involved in this fight were on full display Friday, when the Virginia Supreme Court rejected Attorney General Ken Cuccinelli II’s two-year effort to force the University of Virginia to turn over e-mails, drafts and handwritten notes that prominent climate scientist Michael E. Mann had written while serving on the faculty there. Mann, now a professor at Pennsylvania State University, accused Cuccinelli of engaging in a campaign of “character assassination’’ against him.

There is no question that climate scientists have mobilized in recent years to talk more publicly about greenhouse-gas emissions from activities such as driving and coal-fired power plants. For years there were only a handful of researchers on both sides of the debate: the late Stanford University professor Stephen Schneider and James E. Hansen, who directs NASA’s Goddard Institute for Space Studies, spoke about the risks associated with climate change, while Richard Lindzen, a Massachusetts Institute of Technology meteorology professor, and Roy Spencer, principal research scientist at the University of Alabama at Huntsville, questioned the extent to which humans contributed to the problem.

Now dozens of climate scientists have taken on a more public advocacy role, contending that mounting evidence suggests the world needs to curb greenhouse-gas emissions from the industrial and transport sectors or risk disastrous consequences.

No single event politicized climate researchers more than the posting of more than 1,000 pirated e-mails from the University of East Anglia’s Climatic Research Unit in 2009. The incident, which became known as Climategate, portrayed several prominent researchers as clubby and dismissive of their colleagues. It convinced researchers such as Spencer that his opponents had “crossed a line” by lobbying the editors of scientific journals not to publish the work of climate skeptics.

Several lawmakers and advocacy groups, including the Heartland Institute, seized on those e-mails as evidence that researchers had skewed their results to exaggerate the human contribution to climate change. While several independent inquiries cleared the researchers of any academic wrongdoing, the incident convinced many scientists that they need to make a more public case for why climate change is occuring.

Frumhoff, whose group endorses mandatory limits on greenhouse-gas emissions and enlists scientists to take part in the public debate, said “the willingness of people to be actively engaged has increased dramatically” since the leaked East Anglia e-mails.

The American Geophysical Union, or AGU, offers communications training for its members, along with an annual “Climate Day on the Hill” in which it dispatches them to speak with lawmakers about recent scientific findings, and a $25,000 climate-communication prize. Several scientists have created a “Climate Science Rapid Response Team” to help lawmakers and members of the media reach researchers quickly, while others have raised more than $30,000 for a Climate Science Legal Defense Fund to aid researchers facing either lawsuits or Freedom of Information Act requests over their work.

Several academics who question the notion that human activities are driving dangerous warming said Gleick’s actions show that climate scientists cannot be trusted. William Happer, a Princeton University physics professor who is chairman of the George C. Marshall Institute, wrote in an e-mail that Gleick’s actions demonstrate how radicalized several of them have become.

“Some scientists feel that any hint that something may be rotten in the state of climate is a threat that must be countered by any means possible,” wrote Harper, suggesting that many scientists can fundraise by projecting dire climate impacts. “If you are saving the planet, along with a good funding source, the ends apparently justify the means.”

In an interview, Hansen said he had intentionally withdrawn from the limelight after testifying before the Senate about global warming in 1988. Hansen said he was compelled to reenter the public debate after policymakers failed to act, and he contemplated the prospect that his granddchildren could face a drastically altered planet once they reached adulthood.

He wrote in an e-mail that it is “hard to say” if his outspokeness has affected the way people view his academic work. “The scientific community has its own ways of evaluating the quality of science, so I would hope that it would not make much difference. But I have no choice but to draw attention to the urgency of the situation.”

Hansen delivered another speech on the topic in 2004 and again the following year at an AGU meeting, which generated public attention after NASA officials sought to control his discussions with journalists. He has emerged as one of the most visible advocates for making deep cuts in greenhouse-gas emissions. He was arrested last year in front of the White House protesting the Keystone XL pipeline, a controversial project that would ship energy-intensive crude oil from Canada to the Gulf Coast.

“Scientists ought to connect the dots all the way to the very end,” he said, adding that scientific training often hampers researchers because they are taught to include caveats when they report their findings. “They’re pitted against people who use the talk show method — you just quote these bits of information which support your cause.”

John Abraham, a mechanical engineer at the University of St. Thomas who helped form the rapid response team and filmed a video debunking several claims made by British climate skeptic Christopher Monckton, said many researchers have mobilized because delaying carbon reductions could have “irreversible consequences.”

And now, even the scientists who have argued most forcefully against climate skepticism are worried about the latest act in the climate wars. Earlier this month, Nina Fedoroff, president of the American Association for the Advancement of Science, declared at the annual meeting that she was “scared to death” the world was “slipping back into a dark era” when it came to understanding climate change and other scientific matters.

When asked how the recent uproar would affect the public’s understanding of climate science, Fedoroff replied with just three words: “It doesn’t help.”