the vice president of the United States is to ultimately eliminate all fossil fuel use in the United States. That is their goal. NARRATOR: At the heart of this contentious issue is a battle for the truth. When we strip away the rhetoric and politics, what does science really know about global warming? The question has pushed the once obscure science of climatology into the spotlight. But the climate system has turned out to be very complex. TOM M.L. WIGLEY, Nat'l Center for Atmospheric Research: Now we're getting near the end of the run, where the CO2 level is much more than double present day, and- NARRATOR: And scientists' pronouncements about the future of the planet vary widely as they struggle to determine whether the changes in the climate are natural or caused by human beings. TOM M.L. WIGLEY: A 5-degree warming will just change the whole climate system radically. Precipitation patterns will be entirely different. The amounts of precipitation will be entirely different. PAT MICHAELS, Cato Institute: The climate changes, whether or not human beings have something to do with it. You know, there's- there's this little anomaly called the Ice Age. The Earth's climate naturally goes from its current state to having 5,000 feet of ice over Chicago. The climate is unstable. NARRATOR: Tonight NOVA and FRONTLINE set out to uncover the truth about global warming. A lot is at stake. SEN. FRANK MURKOWSKI, (R) Alaska: Any new climate treaty must not result in serious economic harm to