After an unusual about-face prompted by a late recusal, a federal appeals court has scrapped a ruling that said the nation's largest producers of greenhouse gas emissions could be sued for the damage caused by global warming. The case, Comer v. Murphy Oil, started with a lawsuit by Gulf Coast residents affected by Hurricane Katrina. Claiming that global warming contributed to the severity of the storm, the plaintiffs sued dozens of the nation's largest polluters -- a veritable who's who of utilities, chemical companies and the oil industry.