But more than half of the nation's electricity comes from coal-burning plants.

The answer, however, is not to build more coal-burning plants.

It is released into the air by coal-burning power plants and other sources.

More than 50 percent of the nation's electricity is generated by coal-burning plants.

About 70 percent of its electricity comes from aging coal-burning plants, he said.

The company agreed to cut emissions from eight coal-burning power plants by 70 percent, or 252,000 tons per year, at a cost of $1.2 billion.

He led one of the first states in America to clamp down on old coal-burning electric power plants.

But no one is talking about shutting the region's coal-burning power plants, which account for more than half the pollution.

There is also the question of whether to convert existing coal-burning plants or to construct new ones.

He also has to determine how to deal with mercury that coal-burning plants emit.