What we've often seen is that when we Americans say, look, we've got to reduce pollution, business - some businesses complain about it, but almost every time, it's turned out to be easier and cheaper and accomplished faster, and they've gained confidence, and then we go farther.

We face the gravest threat that civilization has ever confronted. It's global in nature and requires a global solution. Increased CO2 emissions anywhere, whether from China or the United States or from one of the countries that is burning its forests like Brazil or Indonesia.

The insistence on complete certainty about the full details of global warming-the most serious threat we have ever faced-is actually an effort to avoid facing the awful, uncomfortable truth: that we must act boldly, decisively, comprehensively, and quickly, even before we know every last detail about the crisis. Those who continue to argue that the appropriate response is merely additional research are simply seeking to camouflage timidity or protect their vested interest in the status quo.

...the emergent capabilities bursting forth from the revolutionary advances in the life sciences are about to make us the principal agent of evolution.

Someone who expresses a view that is contrary to the view of the overwhelming majority should be allowed to stand undisturbed as a monument to our commitment to free speech.

There are skeptics who do not come to their view because they have a source of income from carbon polluters.

I think that we should ban so-called junk guns. I think we should ban assault weapons like the weapons used here [in Fort Worth], yes. I think that the kinds of weapons that have no legitimate use for hunting or the kind of weapon that a homeowner would use, I think they should be banned, yes, those kind of weapons.