John Christy and Roy Spencer, who won NASA's Medal for Exceptional Achievement for figuring out how to get temperature data from satellites, agree that Earth has warmed. "The thing that we dispute is, is it because of mankind?" Spencer says.

Some scientists say the warming may be caused by changes in the sun, or ocean currents, or changes in cloud cover, or other things we don't understand. If it's all man's fault, why did the Arctic go through a warm period early last century? Why did Greenland's temperatures rise 50 percent faster in the 1920s than they are rising now?

The media rarely ask such questions.

The media also treat the IPCC as impartial scientists, but Reiter and Christy, who were members of the IPCC, say it is not what the public thinks it is. Many of the people involved in writing its report "are not scientists at all," Reiter says. "They were essentially activists." Members of groups like Greenpeace were involved. Skeptics were often ignored.

Christy says, "We were not asked to look at a particular statement and sign our names to it."

Adds Reiter, "I resigned."

But the IPCC still listed him as part of the so-called consensus of scientists. He says he had to threaten to sue to get his name removed from the report, although the IPCC denies that.

Skeptics like Reiter, Christy, Spencer and Tim Ball, who studies the history of climate change and heads the Natural Resources Stewardship Project, are often smeared as "deniers," lumped in with Holocaust deniers and accused of being "on the take" from energy businesses." Gore impugns skeptical scientists by saying "the illusion of a debate has been purchased."

But the scientists I interviewed don't get money from business.

Some get threatened. Ball received an e-mail that said: "You will not live long enough to see global warming!"