For humans, the Arctic is a harshly inhospitable place, but the conditions there are precisely what polar bears require to survive - and thrive. 'Harsh' to us is 'home' for them. Take away the ice and snow, increase the temperature by even a little, and the realm that makes their lives possible literally melts away.

The Earth is a tiny blue speck in a universe of unfriendly options.

Fortunately, we know more about the problems that we have than in all preceding history. We know now the consequences of the things that we put into the air, into the water - of the way we treat life on Earth.

There are now more than 4,000 places in the sea around the world that have some kind of protection. The bad news: You have to look hard to find them. What you find instead is destructive fishing, mining, gas and oil exploration.

We have the power to abstain from destructive behavior.

I've had the joy of spending thousands of hours under the sea. I wish I could take people along to see what I see, and to know what I know.

It's taken us a short time to change the nature of nature. In my lifetime, more change than during all preceding human history put together.