The United States has long thought of itself as the land of infinite plenty, and historically we did have abundant resources. But now we are gradually exhausting our fisheries, our topsoil, our water. On top of that, we're coming to the end of world resources.

Introspection and preserved writings give us far more insight into the ways of past humans than we have into the ways of past dinosaurs. For that reason, I'm optimistic that we can eventually arrive at convincing explanations for these broadest patterns of human history.

Native Americans had only stone and wooden weapons and no animals that could be ridden. Those military advantages repeatedly enabled troops of a few dozen mounted Spaniards to defeat Indian armies numbering in the thousands.

Human societies vary in lots of independent factors affecting their openness to innovation.

Every week in the Senate, I give a speech telling my colleagues it is time to wake up to the reality of a changing climate.

One volcano puts out more toxic gases - one volcano - than man makes in a whole year. And when you look at this 'climate change,' and when you look at the regular climate change that we all have in the world, we have warm and we have cooling spells.

The ocean is this beautiful, unexplored place. Why on Earth everyone isn't down there, I don't know.

The idea of 'climate' - in quotation marks - is never going to be the issue. It's always going to be a local, human issue. And so to the extent that you put 'climate' on the ballot, that's never going to move the needle.