You should ask where your food is coming from.

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.

I personally have stopped eating seafood.

Meat reared on land matures relatively quickly, and it takes only a few pounds of plants to produce a pound of meat.

When I write a scientific treatise, I might reach 100 people. When the 'National Geographic' covers a project, it communicates about plants and fish and underwater technology to more than 10 million people.

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.

Never again will we have this good a chance as we now have to find an enduring place for ourselves within the natural systems that keep us alive. It's a sweet spot in history. That's why this is such a critical time.