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When we meet people who are astronauts or deal in astronomy, it's always really fascinating.

Humans have obviously contributed a great deal of carbon to the atmosphere. So we are warming the planet up.

I think that witnessing ecological problems visible from space is one of the new and essential roles of astronauts.

The sky isn't falling. We're not going to have more meteors hit because of sequestration.

For millions of years, this world has been a great gift to nearly everything living on it, a planet whose atmosphere, temperature, air, water, seasons, and weather were precisely calibrated to allow us - the big us, including forests and oceans, species large and small - to flourish.

It's a wonderful experience to look at our Earth.

The strong evidence is that we're running out of space. We're collectively affecting the world's climate. This is due to the still-growing human population and our increase in consumption.

We're running the most dangerous experiment in history right now, which is to see how much carbon dioxide the atmosphere... can handle before there is an environmental catastrophe.

People get cranky when you burst their bubble. Over time, advances in astronomy have relentlessly reinforced the utter insignificance of Earth on a celestial scale. Fortunately, political and religious leaders stopped barbecuing astronomers for saying so, turning their spits with human-rights activists instead.

Anyone who has spent any time in space will love it for the rest of their lives. I achieved my childhood dream of the sky.