Postcard after postcard came addressed to Naomi Oreskes after she wrote her first book on how scientists study the movement of continents.

A groundswell of attention, perhaps? Not exactly. Her mother wrote them all, dashing off each postcard after finishing a chapter. Outside the worlds of science and academia, the book didn't attract much attention.

But 12 years later, the Manhattan-raised historian is traveling a much more public path, drawing both praise and condemnation. She's a fierce defender of scientists and a leader in the vanguard of those who strongly advocate that the world must acknowledge and deal with global warming.

"Professor Oreskes has turned vilified scientists into the heroes they deserve to be," says John Abraham, an associate professor at the University of St. Thomas in St. Paul, Minn. She's performing a service regarding global warming by showing "how a few organized and influential people were able to confuse the country long after the science was settled," he says.

Oreskes, a professor of history and science studies at the University of California, San Diego, acknowledges that she's trying to save the world. Earlier, though, her goal was simpler. She wanted to understand scientists by studying their past, in terms of both their findings and their funding.

"What difference does it make who pays for scientific research?" she says. "I'm interested in how scientists decide they have enough evidence to say they know something, and what difference it makes who pays for the work. We want science to be objective and neutral, but someone has to pay for it, and there's that old cliché about whoever pays the piper chooses the tune."

After writing about continental drift and plate tectonics, Oreskes began focusing on the efforts of oceanographers.

They were working to better understand the relation between the ocean and the atmosphere. In the process, they uncovered signs of global warming.

"I thought, 'Wow, this is unbelievable, there's this whole history that no one talks about,' " she says. "People have no idea how old the science [of global warming] is."

In 2004, Oreskes wrote a brief paper in the influential journal Science debunking claims that scientists disagreed about global warming. Instantly, she found herself at the center of an emotional dispute. News media cited her work, as did the Al Gore movie "An Inconvenient Truth."

Then, as now, Oreskes offers a simple message backed by extensive documentation: There is no scientific debate over climate change. None, zero, zip.

"The science is stable, the science is real, and there's no reason to doubt climate change," she says.

She followed her Science paper with commentaries in major newspapers, while global warming skeptics bashed her findings, accusing her of ignoring research.

" 'Whoa,' I thought, 'this is really weird,' " Oreskes recalls. "All I did was describe the state of scientific debate. I didn't recommend carbon taxes or comment on emission-trading schemes. All I said was, 'Hey guys, scientists have told us this is happening. Given that it's happening, we should do something about it.' "

Oreskes has since expanded her research beyond climate change. In the 2010 book "Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming," she and coauthor Erik Conway, a historian at the California Institute of Technology, link global warming deniers to a longstanding tradition of science-bashing.

"It's not just about global warming," Oreskes says. "It's really a book about how democracy gets undermined by these doubtmongering campaigns that undermine our ability to understand new problems and find solutions."

Book critics have lauded "Merchants of Doubt," including Will Buchanan, who wrote in a Christian Science Monitor book review that it "might be one of the most important books of the year."

Scientists have praised the book, too. Her work reveals a "sustained disinformation campaign against legitimate climate change science that is well funded, professionally run, and unfortunately, very effective," says Richard Somerville, a professor emeritus at UC San Diego's Scripps Institution of Oceanography.

Oreskes has done more than expose the motivations and strategies of science skeptics, Dr. Abraham says.

"She has provided scientists a well-needed jolt of confidence and energy by showcasing how they are standing up to powers that are unbridled in their attempt to delay climate action," he says. "She has shown how brave these scientists are; she has shown what costs are inflicted upon these scientists; and she has shown that they are not alone."

Abraham himself encountered intense criticism, along with many messages of support, after engaging in what minnpost.com (a website that covers Minnesota news) called a "scientific smackdown" with a British critic of global warming in 2010.

Critics remain unpersuaded by her work. A blogger at americanthinker.com calls Oreskes a "conspiracy queen" who promotes "junk science."

But she continues to dispute the claims of climate change deniers.

"When people say things that are demonstrably false," she says, "you shouldn't be afraid to say that."