Climate change is the greatest threat of our time.

People are not running to build coal facilities because of the price of natural gas, but we do see them being constructed, and there is an interest in fuel diversity, so we took the exercise pretty seriously.

But just [proposing the standard] puts companies on notice that if you're looking to construct a new natural-gas or coal facility, you really need to pay attention to these. This is what they should be designing new facilities toward as soon as this proposal hits the streets.

There is no threshold level of fine particle pollution below which health risk reductions are not achieved by reduced exposure.

Even if there's controversy, I'm going to make the decision, and people are going to be happy in one instance and unhappy in the next. But that's the job I've been given and the job I'm going to embrace.

Greenhouse gas pollution, through its contribution to global climate change, presents a significant threat to Americans health and to the environment upon which our economy and security depends.

Climate change is the greatest threat of our time.