But should he proceed with regulations to control pollution from existing coal-fired power plants, the single largest source of carbon pollution, those regulations probably will contribute to shuttering facilities already struggling to compete with cheap natural gas.

NPR: PROMISES, PROMISES: Climate Change

Tailpipe emissions standards are a much more important issue in California, which has them in place to control pollution from millions of cars, than in North Dakota, which does not have regulations.

FORBES: Magazine Article