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.

I cannot shy away from controversy. I don't know if it's my Irish blood, but I love it.

I don't think any administration, when they come in, thinks that their job is to tell the scientists what the science looks like or to be quiet about the science. Scientists need to remain true and not allow science to be politicized. Scientists are not politicians, and no politician should consider themselves to be a scientist.

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.

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.

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.

Climate change is the greatest threat of our time.