I've spent thousands of hours under water. And even in the deepest dive I have ever made, 2.5 miles (about 4 kilometers) down, I saw trash and other tangible evidence of our presence.

We couldn't go to the moon on whale oil. We don't have the capacity yet to consider doing such things as harnessing current sunlight. We're burning ancient sunlight in order to get us to where we now are. But it's costly.

This is a living planet. Look around. Mars, Venus, Jupiter. Look beyond our solar system. Where else is there a place that works, that is just right for the likes of us? It has not happened just instantly. It is vulnerable to our actions. But it's the result of four and a half billion years of evolution, of change over time. And it changes every day, all the time. It would be in our interest to try to maintain a certain level of stability that has enabled us to prosper, to not wreck the very systems that give us life.

When I arrived on the planet, there were only two billion. Wildlife was more abundant, we were less so; now the situation is reversed.

I have lots of heroes: anyone and everyone who does whatever they can to leave the natural world better than they found it.

Some experts look at global warming, increased world temperature, as the critical tipping point that is causing a crash in coral reef health around the world. And there's no question that it is a factor, but it's preceded by the loss of resilience and degradation.

We are depleting this immense diversity and abundance of life, and it matters tremendously for the future of the planet.