The days of exploration of Shackleton and Scott are long gone. Everything has been climbed, crossed, done. Now what we're exploring are the full boundaries of human endeavour. It's not physical - it's all in the head.

When I was born, the world's population was 3.5 billion. There are now 6.8 billion people on the planet. By 2050, that's expected to rise to 9.4 billion. What's more, the Earth's resources aren't growing; they're decreasing - and rapidly.

We need to save the Arctic not because of the polar bears, and not because it is the most beautiful place in the world, but because our very survival depends upon it.

Normally I don't race other people; I challenge the environment and my own limitations.

When I started researching the eco effects of eating meat, I'd assumed, for no good reason, that environmental irresponsibility would correspond to both animal size and deliciousness: Eating cows would be worst, eating pigs would be a bit less bad, and eating chickens would be basically harmless.

I mean I do believe there is a responsibility of the entertainment industry in general with everything that is happening with the world, with violence and with climate change and with the stereotypes with Latinos or any community.

Let us build a 21st-century rural economy of cutting-edge companies and technologies that lead us to energy and food security. Such an investment will revitalize rural America, re-establish our moral leadership on climate security and eliminate our addiction to foreign oil.

When the government undertakes or approves a major project such as a dam or highway project, it must make sure the project's impacts, environmental and otherwise, are considered. In many cases, NEPA gives the public its only opportunity to be heard about the project's impact on their community.