The global-warming debate is shifting from science to economics. For years, the fight over the Earth's rising temperature has been mostly over what's causing it: fossil-fuel emissions or natural factors beyond man's control. Now, some of the country's biggest industrial companies are acknowledging that fossil fuels are a major culprit whose emissions should be cut significantly over time. A growing number of these companies are pushing for a mandatory emissions limit, or "cap." Some see a lucrative new market in clean-energy technologies. Many figure a regulation is politically inevitable and they want to be in the room when it's negotiated,...