States with tremendous oil and natural gas reserves have the most to gain economically from proper regulation.

I think that one of our most difficult international challenges is clearly climate change and making sure that the Paris agreement goes forward. While I think the international community understands that President Trump is not taking the same position as President Obama.

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

I definitely challenge people. But hopefully, I am working harder than anybody else, and so people won't resent the fact that I want them to work hard, as well.

I think climate change is probably the most extreme, and it's been going on for years because it's very difficult to talk about a planetary issue like climate change and to get people who live within four-year electoral cycles to actually pay attention to something that you predict is happening way in the future.

EPA gets to set a standard for new. For the existing, EPA sets guidelines for what we think is appropriate, but then states develop plans that work for them, taking into consideration their specific energy mix.

We need an international solution to the challenge of climate change, there's no question about it. But the real key is, can you actually get that - or get that solution - without the US' involvement? Can you not lead domestically, and expect the rest of the world will take action... the US needs to lead, we need to be out there.