Every time I slip into the ocean, it's like going home.

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.

When I first ventured into the Gulf of Mexico in the 1950s, the sea appeared to be a blue infinity too large, too wild to be harmed by anything that people could do.

Since I began exploring the ocean in the 1950s, 90 percent of the big fish have been stripped away. Tuna, sharks, swordfish, cod, halibut, you name it, the numbers have just collapsed. Also, about half of the coral reefs are gone, globally, from where they were just a few decades ago.

We must protect our ocean as if our lives depend upon it, because they do.

We have to look in the mirror first. What are we doing? How can we make a change? It always starts with looking in the mirror. Every individual can. Every individual can make a difference either by proactively doing something positive or by doing nothing. That's a decision, too.

The Earth is a unique system in the universe, the only planet we know of that's hospitable for humankind.