Most of the world's major waterways have been diverted or dammed or otherwise manipulated - in the United States, only two per cent of rivers run unimpeded - and people now use half the world's readily accessible freshwater runoff.

There's this idea of shifting baselines. It was coined by a guy named Jeremy Jackson. It's the idea that every generation takes what it sees, and says, "Okay, well, that's the norm."

I don't think there are too many places left that humans haven't pretty thoroughly explored.

One of the reasons that people, many people, many environmentalists are critical of President [Barack] Obama's policies towards global warming is on the one hand he says the right things and he says he's committed to trying to reduce our current emissions.

Several decades ago, a detachment of the American right cut itself loose from reason, and it has been drifting along happily ever since. If the birthers are more evidently kooky than the global-warming "skeptics" or the death-panellers or the supply-siders or the Swift Boat Veterans for Truth, they are, in their fundamental disregard for the facts, actually mainstream.

People sometimes say we need to be really almost on a wartime footing if you want to change. Our whole economy is based on burning fossil fuels, which is taking CO2 out of the ground and putting it up into the air.

Mitochondrial DNA, which is a sort of abridged version of DNA, is passed directly from mother to child, so it's something that can be looked at to trace matrilineal descent.