The debate over global warming is a perfect example of how the integrity of scientific evidence and the credibility of science itself has been compromised in a highly divisive and partisan debate over policy. The most visible proponents of each side present themselves as experts, present their own facts and ignore or undermine the facts of their adversaries. Common ground based on accepted scientific evidence and practices disappears along with deliberative, public dialog. Positions harden. Real uncertainty and risk remain but disappear from view. Subtleties are lost. The public struggles to follow the debate and is mystified, confused.